How reliable are environmental data on ‘orphan’ elements? The case of bismuth concentrations in surface waters

Abstract

Like all elements of the periodic table, bismuth is ubiquitously distributed throughout the environment as a result of natural processes and human activities. It is present as Bi(III) in environmental, biological and geochemical samples. Although bismuth and its compounds are considered to be non-toxic to humans, its increasing use as a replacement for lead has highlighted how little is known about its environmental and ecotoxicological behaviour. In this first critical review paper on the existing information on bismuth occurrence in natural waters, 125 papers on fresh and marine waters have been collated. Although the initial objective of this study was to establish the range of the typical concentrations of total dissolved bismuth in natural waters, this proved impossible to achieve due to the wide, and hitherto unexplained, dispersion of published data. Since analytical limitations might be one of the reasons underlying value dispersion, new analytical methods published since 2000—intended to be applied to natural waters—have also been reviewed. Disappointingly, the detection limits of the bulk of them are well above those required; they are thus of limited usefulness. Analysis of the existing information on bismuth in secondary references (i.e., books, review chapters) and on its chemical speciation in seawater revealed that the uncritical reproduction of old data is a widespread practice.

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Montserrat Filella

Montserrat received her PhD in Chemistry from the University of Barcelona in 1986. She teaches Environmental Chemistry at the University of Geneva, where she arrived in 1987. Since 2007 she also works in the development of a society specialised on fundamental research in environmental chemistry in Luxembourg. She is an IUPAC fellow and member of a number of scientific societies. Her main research interests focus on the understanding of the physicochemical processes regulating the behaviour of chemical elements in environmental and biological compartments. The three main axes of her research concern the study of: colloids in natural waters, natural organic matter and Group 15 elements.

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Environmental impact

Bismuth has been qualified as an “amazingly ‘green’ environmentally-minded element”. In the early 1990s, research began on the evaluation of bismuth as a non-toxic replacement for other more noxious elements, particularly lead. The introduction of bismuth in some of these applications, and in particular the approval of bismuth-tin shot for waterfowl hunting, has been accompanied by the ‘discovery’ that actually very little is known about the ecotoxicology of the element. Similarly, its environmental chemistry remains poorly understood. As a first step to identify the areas of environmental bismuth chemistry that need to be preferentially addressed, this study critically analyses published values of total concentrations in surface waters as well as the scarce existing information on bismuth speciation in aquatic systems.

1. Introduction

Bismuth is a naturally occurring element. It is the heaviest element in Group 15 of the Periodic Table of Elements. Bismuth can exist in a variety of oxidation states (−III, 0, III, V). Since Bi(V) is a powerful oxidant in aqueous solution, bismuth is found in the trivalent oxidation state in environmental, biological and geochemical samples. This is in stark contrast to other Group 15 elements, such as arsenic and antimony, for which the pentavalent state is the most abundant.

Bismuth has no known biological role. It is an element which is relatively non-toxic to humans in comparison to the metals and metalloids surrounding it in the periodic table (i.e., polonium, tellurium, antimony, tin and lead). However, bismuth is toxic to some prokaryotes, and bismuth compounds have been used for more than 200 years to treat ailments resulting from bacterial infections.

Little information is available on the transformation and transport of bismuth in the different environmental compartments and even information on total bismuth content in the various environmental media is scarce and often contradictory, as evidenced in this study which gathers and analyses published values of bismuth concentrations in seawater and freshwater.

2. Why bismuth?

Bismuth has been a largely neglected element in environmental studies. Two reasons can be put forward: (i) the low concentration of bismuth in environmental systems, often justified on the grounds of the insolubility of its compounds; (ii) the renowned low toxicity of the element to humans. Bismuth has even been qualified as an “amazingly ‘green’ environmentally-minded element” in a report of the Bismuth Institute,¹ a Brussels-based information centre for industry that ceased to exist in 2002. In the early 1990s, research began on the evaluation of bismuth as a non-toxic replacement for other more noxious elements, particularly lead, in such uses as fishing sinkers, plumbing, lubricating greases, ceramic glazes, pigments, food-processing equipment, and shot for waterfowl hunting. The introduction of bismuth in some of these applications, and in particular the approval of bismuth-tin shot for waterfowl hunting,² has been accompanied by the ‘discovery’ that actually very little is known about the ecotoxicology and the environmental behaviour of the element.^3–5 Thus it is now useful to establish what is already known in order to guide further research. Moreover, our environmental understanding of companion elements, such as other group 15 elements (i.e., arsenic, antimony) or elements which are difficult to study (e.g. polonium), will also benefit from a better understanding of bismuth behaviour. The growth of new ‘green’ applications should not make us forget, however, that bismuth is already used in a wide variety of applications, such as over-the-counter and prescription medications (e.g., treatment of ulcers and other gastrointestinal disorders, syphilis, dermatological disorders, radiotherapy), cosmetics (e.g., nail varnish, lipstick, hair dye), catalysts, low melting alloys in automatic fire-sprinkler systems or electric fuses, metallurgical additives, semiconductors, etc. World production in 2007 was estimated at 6,300 metric tones.⁶ In 2003 (the last year for which data are available), apparent consumption of Bi in the US distributed among end-use categories was as follows: 46% fusible alloys, solders and cartridges; 35% pharmaceuticals and chemicals; 17% metallurgical additives, and 2% other industrial uses.⁶

3. Published concentrations

Like any other chemical element, bismuth is present in the aquatic environment as a result of rock weathering, soil runoff and anthropogenic activities. It is of interest to mention that it has been suggested that bismuth could be used as a tracer of volcanic emissions⁷ due to the higher concentration of bismuth in volcanic emissions compared with its other natural and anthropogenic sources.^8–11

3.1. Marine systems

Published concentrations of Bi in seawater have been collected. They are shown in Table 1. All values come from original sources; multi-referencing has been avoided. Results are reported in the original units and, when possible, also in a common unit scale (ng L⁻¹) to facilitate value comparison. This table includes results from three types of studies: (i) the very few studies explicitly devoted to the study of the behaviour of Bi in seawater (BI in the table); (ii) environmentally-oriented studies where a certain number of elements, including Bi, are simultaneously measured (ENV); (iii) studies that describe the development of a new analytical method that is applied to seawater samples (ANAL). The fact that so few studies have been exclusively dedicated to Bi (i.e., 3 out of 38) indicates the limited interest that this element has garnered up to now. It should be mentioned that analytically-oriented papers rarely contain enough complementary information about the system sampled for the data to be useful from an environmental point of view.

Table 1 Published bismuth concentrations in seawater

System^a		Complementary information	Dissolved Bi^b original units	Units	Dissolved Bi/ng L^−1	Particulate Bi	Sample acidification	Filtration	Experimental technique^c	DL^d/ng L^−1	Type of study^e	Ref.
a International country codes follow the ISO 3166 convention; specific sampling dates are only given when they are needed to differentiate samples. b n = number of analysis; BDL = below detection limit; DL = detection limit; CL = 95% confidence limits; RSD = relative standard deviation. c See corresponding list for meaning of abbreviations. d DL = detection limit. e Type of study: BI = environmental study devoted to Bi only, ENV = environmental oriented study but not devoted to Bi only, ANAL = analytical method development study where Bi concentrations have been measured in real samples but no ancillary environmental data about the system are given.
Gullmar fjord, SE, summer 1937			0.2	μg L^−1	200		—	not mentioned	Co-precipitation	—	ENV	12
									Spectrographic method
South African coastal water			0.017	mg tonne^−1	17		0.1 M in HCl	sedimentation bottle + cotton-wool plug	Anion-exchange (Amberlite IR-400, 100 days, 250 L) of the 0.1 N HCl acidified sample	not given	ANAL	13
									Emission spectroscopy of evaporated and ashed resin
English Channel (50° 02′ N 4° 22′ W), surface water			0.024, 0.026 (n = 2)	μg L^−1	24, 26		0.1 M in HCl	Whatman glass-fibre filter (GF/B)	Anion exchange (De-Acidite FF) of the 0.1 N HCl acidified sample	not given	ANAL	14
Irish Sea, surface water		2 samples	0.042, 0.035		42, 35
North Atlantic (45° 07′ N 7° 38′ W):									Photometric determination with dithizone
	surface water		0.033		33
	2000 m depth		0.015		15
Jervis Bay, New South Wales coast, AU		3 samples collected 4 months apart	0.21 ± 0.02 (n = 2)	μg L^−1	210	0.011 ± 0.002 (n = 2)	pH < 2 (0.02 M in HCl)	0.45 mm Millipore filter (HAWP 047 00)	ASV on a glassy carbon mercury coated electrode	not given	ANAL	15
			0.13 ± 0.02 (n = 2)		130	<0.005 (n = 2)			Particulate digestion: filter wet-ashing with 2 mL 15 M HNO3 and 1 mL 72% HClO4
			0.043 ± 0.02 (n = 2)		43	<0.005 (n = 2)
						All in μg L^−1
Boston Light-Ship, US			0.015 (CL: 43%, n = 3)	μg kg^−1	15		0.1 M in HCl	not mentioned	MCGE-ASV (pH 0.5–1.5)	4	ANAL	16
Pacific deep water, Baja, California, US			0.040 (CL: 42%, n = 3)		40		pH 1.67 (HCl)
Bahia Honda Key, FL, US		4 samples	0.090 (CL: 6%, n = 3)		90		1 M in HCl
			0.086 (CL: 31%, n = 3)		86
			0.094 (CL: 4%, n = 3)		94
			0.080 (CL: 25%, n = 3)		80
New South Wales and Queensland coastal waters, AU:				μg L^−1			0.05 M in HCl	0.45 μm Millipore filter (HAWP 047 00)	ASV on a glassy carbon mercury coated electrode	not given	BI	17
	Botany Bay		0.11, 0.11		110, 110	0.002
	Jervis Bay		0.045, 0.043		45, 43	0.002			Particulate digestion: filter wet-ashing with 2 mL 15 M HNO3 and 2 mL 72% HClO4
	Jervis Bay		0.045		45	—
	Jibbon Beach		0.018, 0.021		18, 21	<0.001
	Jibbon Beach		0.041 ± 0.003 (n = 7)		41	0.005
	Jibbon Beach		0.038		38	—
	Queensland		0.12, 0.10		120, 100	<0.001
						All in μg L^−1
Standard sea water sample (origin unknown)			<0.01 (DL)	ppb	<10		—	not mentioned	ASV on a glassy carbon mercury coated electrode	10	ANAL	18
North Sea, off the Belgian Coast, 3 m depth		5 samples	0.20, 0.68, 0.55, 0.20, 0.28	ppb	200, 680, 550, 200, 280		not mentioned	0.8 μm Millipore filter	HMDE-DPASV (pH 1, 1.2 M HCl)	50	ANAL	19
Sea water, 34° 25′ N 133° 54′ E (Shibukawa, Okayama Prefecture, JP)			0.010 ± 0.002 (n = 4)	μg L^−1	10		not mentioned	not mentioned	Flotation (surfactant: sodium dodecyl sulfate and sodium oleate) of Bi co-precipitated with iron(III) hydroxide	not given	ANAL	20
									HG-AAS
Kattegatt surface seawater:				pM			not acidified, NaOH added	not mentioned	Co-precipitation with Mg(OH)2, centrifugation (1200 rpm, 10 min) , centrifugation (1200 rpm, 10 min)	not given	ANAL	21
	N 56° 33.3, E 12° 53.6		13 ± 7 (n = 8)		2.7
	N 57° 36.6, E 11° 53.4		7 ± 3 (n = 4)		1.5
	N 57° 38.9, E 11° 52.2		7 ± 1 (n = 4)		1.5				PSA
Pacific Ocean (17° 30′ N, 109° 00′ W), water depth 3550 m:				ng L^−1			pH 2 (HCl)	0.45 μm Millipore filter	Precipitation with 6 M NaOH, decantation	0.003	ANAL	22
	surface Oct 31, 1981		0.053		0.053				HG-AAS
	2500 m below surface Nov 3, 1981		<0.003 (DL)		<0.003
Scripps Pier, La Jolla, CA, US:
	Oct 15, 1981		0.052		0.052	0.13 (total)
	Jan 4, 1982		0.085		0.085	0.29 (total)
San Diego Bay, San Diego, CA, US, Dec 18, 1981			0.63		0.63	2.0 (total)
Mission Bay, San Diego, CA, US, Dec 18, 1981			0.46		0.46	1.6 (total)
						All in ng L^−1
Pacific ocean coastal waters, JP:				ng mL^−1			10 mL HNO3 per 1 L sample	not mentioned in the English abstract	Extraction of the Bi- DEDTC complex in CCl4, rotary evaporation of the solvent, rotary evaporation of the solvent	4	ANAL	23
	Hitachi		0.026		26
	Tkai		0.032		32
	Isozaki		0.030		30				GFAAS
	Oarai		0.025		25
North Sea (Belgian Coast)		same sample, several methods	0.05	μg L^−1	50		not mentioned	0.45 μm filter	HMDE-DPASV, pH 1.15	not given	ANAL	24
			0.05		50				HMDE-DPASV + SO2
			0.10		100				HMDE-DPASV + UV + SO2
			0.011		11				RRDE-ASV, pH 1.15
			0.014		14				RRDE-ASV + SO2
			0.13		130				RRDE-ASV + UV + SO2
North Atlantic seawater (surface samples and profile down to 2800 m)		19 samples	12 ± 9	pM	2.6		not acidified, NaOH added	not mentioned	Co-precipitation with Mg(OH)2, centrifugation (1200 rpm, 10 min), centrifugation (1200 rpm, 10 min)	1	BI	25
									PSA
Transect North Atlantic and Caribbean:				fmol kg^−1			yes but no details given	not mentioned	HG-AAS as in [22]	not given	ENV	26
	Coastal waters		250		0.052
	Sargasso Sea		340		0.071
	Caribbean		250		0.052
	Both sides Panama Basin		<150		<0.031
	off Bermuda waters		290		0.061
North Sea, off the Belgian coast, Jul 83		19 stations	<0.005 (DL) except close to the coast and in the vicinity of Scheldt estuary:	μg L^−1			not mentioned	not mentioned	HMDE-DPASV, RRDE-DCASV	5	ANAL	27
			0.005 – 0.014 (acid)		5 – 14				Two types of results depending on method used to destroy NOM: acid and UV
			0.070 – 0.150 (UV)		70 – 150
Profiles in the North Pacific (coast of California out to the N of Hawaii)		surface (20 m)	89	fmol kg^−1	0.019		pH < 2 (4 mL 6 M HCl in 1 L sample)	not mentioned	Anion exchange (AG1-X2) of the 0.1 N HCl acidified sample	not given	BI	28
			94		0.020
			99		0.021
			113		0.024
			152		0.032				HG-AAS
			171		0.036
		1000 m depth	268		0.042
			200		0.047
			225		0.037
			178		0.056
		5500 m depth	28		0.006
Profiles in several locations in the Atlantic		surface (10 m)	453		0.095
		1032 m depth	177		0.037
		4855 m depth	115		0.024
Coastal regions, CN		1094 sampling stations	(0.95 ± 0.25)×10^−11	M	2.0		not mentioned	0.45 μm filter	HMDE-ASV	not given	ENV	29
			(0.7 – 1.2)×10^−11
Tokyo Bay, JP:				ng L^−1			pH 2 (HCl)	not mentioned	Precipitation with 6 M NaOH, filtration (0.40 μm)	1 ng (in?)	ANAL	30
	16 Sep 1986	5 samples	1.0, 2.1, 1.5, 1.0, 0.6		1.0, 2.1, 1.5, 1.0, 0.6
	8 Dec 1986	1 sample	1.5		1.5				HG-AAS
Coast of Heligoland			12 ± 2	ng L^−1	12		not mentioned	not mentioned	SW-ASV (glassy-carbon RDE)	2	ANAL	31
Palaea Kameni hydrothermal waters, Santorini, GR			<0.8 (DL)	μg L^−1	<800		not mentioned	not mentioned	Reference given (conference proceedings)	800	ENV	32
Kanazawa City, JP:				ng L^−1			18 mL HNO3 in 1 L sample	0.45 μm Millipore filter	Preconcentration: sorption on thionalide-loaded silica gel	100?	ANAL	33
	Sai River		2.4		2.4				HG-AAS
	Tatsumi canal		3.4		3.4
	Asano River		BDL		BDL
Pacific Ocean (33° 17′ 33′′ N 134° 13′ 1′′ E), 2.7 km off-shore, 320 m depth			0.161 (RSD: 2.2%, n = 3)	ng L^−1	0.161		pH 1.5 (HCl)	unfiltered	Solvent extraction: triisooctylamine in heptane, pH = 1.5	3	ANAL	34
Pacific Ocean (36° 57′ N 140° 51′ 53′′ E):
	1 m depth		0.453 (RSD: 2.1%, n = 3)		0.453				ICP-MS
	99 m depth		0.471 (RSD: 1.8%, n = 3)		0.471
Isozaki coast (36° 22′ 40′′ N, 140° 37′ 56′′ E), JP			1.6 (RSD: 6.9%, n = 4)	ng L^−1	1.6		0.1 M in HCl	0.45 μm Millipore filter (after acidification)	Solvent extraction: sodium diethyldithiocarbamate in xylene	0.27	ANAL	35
Hitachi harbour (36° 28′ 27′′ N, 140° 37′ 50′′ E), JP			1.6 (RSD: 6.2%, n = 4)		1.6				ETAAS
Seawater, Chiba, Katsuura City, JP			0.0125 (RSD: 4.0%, n = 4)	ppb	12.5		not mentioned in the English abstract	not mentioned in the English abstract	Co-precipitation with zirconium hydroxide; filtration	10	ANAL	36
									DP-ASV
Buzzards Bay, MA, US						0.038 pM	not mentioned	0.2 μm filter	CFF: fraction 1 kDa–0.20 μm	not given	ENV	37
									Evaporation, dissolution HNO3
									ICP-MS
NRCC NASS-3 (open seawater)			0.014 ± 0.002 (n = 5)	ng mL^−1	14			—	VG-ETV-ICP-MS with in situ preconcentration in a Pt-coated GF	3	ANAL	38
Seawater (no details given)			12 ± 2	ppb	12 000		0.1 M HNO3	0.45 μm Millipore filter (after acidification)	Preconcentration: polyurethane column packed with F2H2Dz	10 000	ANAL	39
									Flameless AAS
Chinese certified seawater GBW(E) 080040			0.0036 ± 0.0005 (n = 6)	ng mL^−1	3.6		pH 2 (HNO3)	0.45 μm Millipore cellulose membranes (probably after acidification)	Preconcentration: poly(acrylaminophosphonic – dithiocarbamate) fibre; elution and evaporation to near dryness	0.155	ANAL	40
Coast of China, 1 m depth samples:				ng L^−1
	Tianjin seawater		8.70		8.70
	Dalian seawater		8.10		8.10				ICP-MS
	Qingdao seawater		3.09		3.09
	Qinghuangdao seawater		11.4		11.4
Chinese certified seawater GBW(E) 080040			0.0037 ± 0.0005 (n = 6)	ng mL^−1	3.7		pH 2 (HNO3)	0.45 μm Millipore cellulose membranes (probably after acidification)	Preconcentration: sorption onto 8-hydroxyquinoline immobilized polyacrylonitrile hollow fibre membrane	31	ANAL	41
Coast of China, 1 m depth samples:				ng L^−1
	Tianjin seawater		8.85		8.85
	Dalian seawater		7.88		7.88				ICP-MS
	Qingdao seawater		3.01		3.01
	Qinghuangdao seawater		11.9		11.9
Ise Bay (1 km off-shore Nagoya port), JP			0.0017	μg L^−1	1.7		pH 1 (HNO3)	0.45 μm membrane filter	Preconcentration by chelating resin (Chelex 100) adsorption	0.03	ANAL	42
									ICP-MS
									Less than 50% recovery
Sea water (no details given)		6 samples	0.54 ± 0.05	μg L^−1	540		not mentioned	not mentioned	HG-ETAAS	70	ANAL	43
			0.30 ± 0.05		300
			<0.24		<240
			<0.24		<240
			0.26 ± 0.05		260
			0.33 ± 0.05		330
Bosphorous seawater			0.0048 ± 0.0008 (n = 3)	mg L^−1	4800		5 mL HNO3 added to an unknown sample volume	not mentioned	SPE: silica gel modified with 3-aminopropyltriethoxysilane	800	ANAL	44
									GF-AAS
Marmara Sea, near Istambul, TR		heavily polluted	0.053 ± 0.002 (n = 5)	mg L^−1	53 000		not mentioned	0.45 μm Millipore cellulose membrane filter	SPE: Chromosorb-107	500	ANAL	45
									GF-AAS
Ise Bay (1 km off-shore Nagoya port), JP			0.00038 ± 0.00002 (n = 3)	μg L^−1	0.38		pH 1 (HNO3)	0.45 μm membrane filter	Tandem preconcentration using a chelating resin (Chelex 100)	0.05	ANAL	46
									ICP-MS
Gulf of Bengal close to Pulicat Lake, IN:				μg L^−1			5 mL HNO3 in 1 L sample	0.45 μm cellulose membrane filter (after acidification)	SPE: piperidene dithiocarbamate-coated Amberlite XAD-7 resin	1200	ANAL	47
	Sea water 1		1.4 ± 0.08 (n = 5)		1400
	Sea water 2		BDL						ICP-MS
Shibukawa Sea, Okayama, JP			22.9 ± 0.5 (n = 5)	pg mL^−1	22.9		not mentioned	not mentioned	Preconcentration: glycine-type chitosan resin	0.1	ANAL	48
									ICP-MS
Shibukawa Sea, Okayama, JP			0.023 ± 0.000	ng mL^−1	23		not mentioned	not mentioned	Preconcentration: chitosan resin functionalized with CCTS-DHBA	not given	ANAL	49
Shin Okayama Port, Okayama, JP			0.018 ± 0.001		18				ICP-AES

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Because of their possible strong influence on the reported results, filtration details are given when available (unfortunately, nearly 50% of the studies neglect to mention whether the samples have been filtered or not). The limit of detection of the analytical methods applied as well as information about acidification of samples are also provided, as they can help to evaluate the reliability of the associated results. As readily observed in Table 1, the dispersion of published results is very high. Even if extremely large values—very probably due to external contamination during sampling or analysis—are not considered, value dispersion remains high and cannot be accounted for by the fact that values from coastal zones, more prone to the effects of man-made pollution, have also been included in the table. Interestingly, there is no clear trend linking the concentration values with the year of publication nor, in particular, is any decrease in the measured concentrations observed, as is the case for other elements. On the basis of the published values, and considering the apparent quality of the different studies, it could be safely stated that bismuth was present in seawater at a 10–30 ng L⁻¹ concentration level, if the often-referenced, and usually well-considered, values of Lee and co-workers^22,26,28 were not about three orders of magnitude lower. Interestingly, these authors^22,28 found a significant proportion of the total Bi, ca. 70%, in particulate form and reported fairly dynamic behaviour of the element in seawater. The predominant presence of bismuth associated to particles might help to explain Lee's low values but is of no assistance in determining whether other reported values are too high because they include some colloidal Bi as ‘dissolved’, which Lee also does partly by filtering at 0.45 μm, or whether Lee's preconcentration methods ‘lose’ some ‘dissolved’ bismuth.. 70%, in particulate form and reported fairly dynamic behaviour of the element in seawater. The predominant presence of bismuth associated to particles might help to explain Lee's low values but is of no assistance in determining whether other reported values are too high because they include some colloidal Bi as ‘dissolved’, which Lee also does partly by filtering at 0.45 μm, or whether Lee's preconcentration methods ‘lose’ some ‘dissolved’ bismuth.

3.2. Freshwater systems

The distribution of bismuth in freshwater systems has not been extensively studied. For instance, not a single study has ever been devoted exclusively to the study of Bi. Published results on bismuth concentrations in freshwaters are shown in Table 2. The same complementary information as in Table 1 is given. Concentrations range from a few ng L⁻¹ to a few μg L⁻¹. In theory this reflects the wide range of geochemical conditions existing in freshwater systems and the proximity of sources of pollution but, in practice, analytical limitations very probably also have an impact on the observed dispersion. It is thus not possible, on the basis of the current data, to safely establish a background concentration range for Bi in freshwaters.. In theory this reflects the wide range of geochemical conditions existing in freshwater systems and the proximity of sources of pollution but, in practice, analytical limitations very probably also have an impact on the observed dispersion. It is thus not possible, on the basis of the current data, to safely establish a background concentration range for Bi in freshwaters.

Table 2 Published bismuth concentrations in freshwater systems

System^a		Complementary information	Dissolved Bi^b original units	Units	Dissolved Bi/ng L^−1	Particulate Bi	Sample acidification	Filtration	Experimental technique^c	DL^d/ng L^−1	Type of study^e	Ref.
a International country codes follow the ISO 3166 convention; specific sampling dates are only given when they are needed to differentiate samples. b n = number of samples; CV = coefficient of variation; RSD = relative standard deviation. c See corresponding list for meaning of abbreviations. d DL = detection limit. e Type of study: BI = environmental study devoted to Bi only, ENV = environmental oriented study but not devoted to Bi only, ANAL = analytical method development study where Bi concentrations have been measured in real samples but no ancillary environmental data about the system are given.
Waters from 15 regions of Siberia, RU		2666 samples (Bi found in 13 samples)	0.0001–0.0054	mg L^−1	100–5400		not mentioned	not mentioned	Precipitation (sodium sulfide and aluminium hydroxide)	not given	ENV	50
									Spectrographic method
Antarctica highly saline lakes (McMurdo Oasis):				μg L^−1			not mentioned	not mentioned	pH 3 (HCl), oxidation with Cl2 gas, extraction with cyclohexane, tar ashing at 450 °C gas, extraction with cyclohexane, tar ashing at 450 °C	not given	ENV	51
	Lake Vanda		6.1		6100
	Lake Bonney		7.1		7100
	Lake Fryxell		<2		<200
	Lake Joyce		3.8		3800				Spectrographic method
	Lake Hoare W lobe		<2		<200
	Lake Hoare E lobe		<2		<200
Lake Miramar, San Diego, CA, US			<0.15	ng L^−1	<0.15	<0.15 (total)	pH 2 (HCl)	0.45 μm Millipore filter	Precipitation with 6 M NaOH, decantation	0.003	ANAL	22
Rain Water, La Jolla, CA, US			0.62		0.62	3.2 (total)
						All in ng L^−1			HG-AAS
Raw water			<0.05 (filtered 0.45 μm)	μg L^−1	<50	0.06 ± 0.03 (total)	pH 1.5–1.7 (HCl or HNO3)	0.45 μm and 2 nm filters	Stripping voltammetry	not given	ENV	52
			<0.05 (ultrafiltered)			0.12 ± 0.06 (total)
Drinking water			<0.05 (filtered 0.45 μm)		<50	All in μg L^−1
			<0.05 (ultrafiltered)
Douglas River drainage system affected by U mining, CA		7 sampling points over 5 years (1982–1986)	<5.0 (except in the mine effluent and occasionally in a few sampling points)	μg L^−1	<5000		1% in HNO3	unfiltered	AAS	5000	ENV	53
Great Lakes (surface water):		median values		ppb			5 mL HNO3 in 1 L sample	0.5 μm Teflon filter	Particulate digestion: 10% HNO3 and 30% H2O2, 80 °C, 4 h	not given	ENV	54
	Lake Huron, 1981		0.86		860	0.079
	Lake Erie, 1981		0.69		690	0.23
	Lake Michigan, 1981		0.81		810	0.020
	Lake Superior, 1983		0.13		130	0.0050			HG-AAS
	Lake Ontario, 1981		1.4		1400	0.34
	Lake Ontario, 1985		0.27		270	0.0078
						All in ppb
Tap water, DK			79 (n = 3)	nM	16 500		not mentioned	not mentioned	Voltammetry with a CME (graphite paste containing 1-(2-pyridylazo-2-naphthol)	21	ANAL	55
NBS-SRM 1643 b			51 (n = 4)		10 600
Tap water, Warsaw, PL		2 samples	0.19	μg L^−1	190		pH = 1 (HCl)	unfiltered	UV irradiation and reduction with hydrazine	20	ANAL	56
Vistula River, PL		6 samples	0.31 ± 0.03		310				HMDE-DP-ASV
Amazonian waters, BR:				μg L^−1			5 mL HNO3 in 500 mL sample	0.2 μm Nucleopore membranes (after acidification)	ICP-MS	not given	ENV	57
	Rio Negro	8 samples	<0.02 (all)		<20
	Rio Solimões	8 samples	<0.02 (3), 0.05, 0.04, 0.06, 0.2, 0.06		<20–60
	Shield streams in Carajás	8 samples	<0.02, <0.04 (6), 0.06		<20–60
Spring water, Oodaki town, JP			0.071 (RSD: 6.30%, n = 4)	ppm	71 000		not mentioned in the English abstract	not mentioned in the English abstract	Co-precipitation with zirconium hydroxide; filtration	10	ANAL	36
River water, Chiba, Youro valley, JP			0.012 (RSD: 8.30%, n = 4)		12 000				DP-ASV
Norwegian hard rock groundwater:		145 samples	median = 0.001	μg L^−1	1		not acidified	unfiltered	ICP-MS	1	ENV	58
	Oslo		0.001						Surface water values come from reports
	Bergen		0.001
Norwegian surface waters		473 samples	median <0.02
Finnish surface waters		several hundred samples	median = 0.005
Ob River, RU		17 samples	0.04 (CV = 0.63)	μg L^−1	40		not mentioned	‘blue ribbon’ paper filter	Voltammetry	10	ENV	59
Major tributaries Ob River, RU		12 samples	0.14	μg L^−1	140		not mentioned	not mentioned	not given	not given	ENV	60
Marmato District (Au mining), CO:							not mentioned	not mentioned	Particulate digestion: strong acid (not given)	2 × 10^6	ENV	61
	Marmato district (summer)	8 samples				<2–30
	Marmato district (winter)	4 samples				<2–34			Analytical technique not given
	Cauca River (summer)	5 samples				<2–2
	Cauca River (winter)	6 samples				<2–2
						All in ppm
Alkaline lakes in the Sasykkul depression, East Pamirs, TJ:				ng L^−1			pH 3 (HNO3)	0.4 μm membrane filter	Co-precipitation: CdS in the presence of FeCl3, filtration (no conditions given), drying, filtration (no conditions given), drying	0.1	ENV	62
	Tuzkul Lake		0.7		0.7
	Sasykkul Lake		2.8		2.8				Emission spectrochemical analysis
Bulunkul Lake (fresh lake), TJ			1.1		1.1
56 European bottled mineral waters			median = 0.001 (<0.001–0.024)	μg L^−1	1		not acidified	unfiltered	ICP-MS	1	ENV	63
Lakes in the Kola Peninsula, RU		120 lakes	<0.02	μg L^−1	<20		not acidified	unfiltered	ICP-MS	not given	ENV	64
Crystalline bedrock groundwaters, NO		476 samples	median <0.001	μg L^−1	<1		4 mL conc HNO3 in a 400 mL sample	unfiltered	ICP-MS	1	ENV	65
			max = 3.2
Groundwater Wells El-Menoufia, Nile Delta, EG		4 samples	1, 0.2, 0.2, 0.4	μg L^−1	1000, 200, 200, 400		HCl added, pH not given	0.45 μm cellulose acetate membrane filter	HMDE-DPASV	38	ANAL	66
River Elbe, DE		18 samples				1.05 ± 0.09 μg g^−1	not mentioned	0.45 μm-Nucleopore filters	Particulate digestion: HNO3/HF high-pressure with microwave induction	not given	ENV	67
									TXRF or ICP-AES or ICP-MS or INAA
Vicinity of a Cu–W mine, Dalsung mine, KR		17 samples	<1	μg L^−1	<1000		pH < 2 (HCl)	0.45 μm membrane filter paper	Particulate digestion: fuming HNO3 and Mg(NO3)2	not given	ENV	68
									HG-ICP-AES
Llobregat River, ES		93 samples (3 sampling points, Jul 96–Dec 2000)	<0.08	μg L^−1	<80		1% HNO3 (v/v)	unfiltered	ICP-MS	not given	ENV	69
Salí River watershed, AR		110 samples (37 sampling points, 4 sampling campaigns)	<0.08	μg L^−1	<80		1% HNO3 (v/v)	unfiltered	ICP-MS	not given	ENV	70
Tap water			6.2	ng mL^−1	6200		not mentioned	not mentioned	HMDE-ASV using morin as a complexing agent	4500	ANAL	71
Groundwater in a closed-basin aquitard, La Laguna Region, MX:				mg L^−1			pH < 2 (HNO3)	not mentioned	ICP-AES or ICP-MS	not given	ENV	72
	Spring	1 spring	0.002		2000
	Carbonate aquifer	6 wells	0.0002–0.005		200–5000
	Thin alluvial fan	2 wells	0.002, 0.005		2000, 5000
	Aquitard	6 brine production wells	0.02–0.04		20 000–40 000
Lakes, ponds and reservoirs, TW and offshore islands		50 samples	<3	ppb	<300		yes but no details given	0.45 μm Nalgene filter	ICP-MS	300	ENV	73
Mouth of the St. Lawrence River, CA		13 samples	0.7 ± 0.3	ng L^−1	0.7	0.29 ± 0.11 μg g^−1	pH 2 (HNO3)	0.45 μm polycarbonate membrane and polypropylene filters	ICP-MS	not given	ENV	74
									Particulate: filter digestion with 2 mL conc. HNO3 and 1 mL HF
Tap water			0.23 (RSD 5.2%, n = 5)	μg L^−1	230		not mentioned	not mentioned	CPE-ASV using BPR as complexing agent	104	ANAL	75
River water 1			0.42 (RSD 3.9%, n = 5)		420
River water 2			0.67 (RSD 2.8%, n = 5)		670
Lake Van, TR		10 locations (each n = 3)	63.1 ± 43.1 (14–110)	ppb	63 100		0.02 M HNO3	blue-band paper filter	Bi-DEDTC complex sorbed onto activated C	not given	ENV	76
Rivers flowing into Lake Van, TR		5 rivers (each n = 3)	45.2 ± 35.8 (7–96)		45 200				FAAS
River water (no details given)		5 samples	1.19, 0.74, 0.43, 0.39, 0.00	ng mL^−1	1190, 740, 430, 390, 0		not mentioned	not mentioned	SPE: XAD-4-salen; filtration Whatman # 2	not given	ANAL	77
									GF-AAS
Tap water, Arak, IR			0.160 ± 0.01 (n = 3)	ng mL^−1	160		pH 3.0–3.5 (dil. H2SO4)	0.45 μm filter	Cloud point extraction (surfactant: Triton X-114, complexing agent: ditizone)	20	ANAL	78
									ET-AAS
River water certified reference material (JSAC 0301-1)			0.000053 ± 0.000009 (n = 5)	μg L^−1	0.053		—	not mentioned	Preconcentration: chelating resin (Chelex 100)	0.01	ANAL	79
									High efficiency nebulization ICP-MS
									High blank value
Tap water, Arak University, Arak, IR			3.5 ± 1.2	ng mL^−1	3500		not mentioned	not mentioned	HMDE-ASV stripping using TPN as complexing agent	800	ANAL	80
Duero Cenozoic basin, ES (As-rich groundwater)		514 water samples (groundwater and springs)	BDL–0.05	μg L^−1	BDL–50		not mentioned	not mentioned	ICP-MS	not given	ENV	81
Nainital, IN:		18 locations		ppb			not mentioned	not mentioned	Co-precipitant and internal standard: PdCl2, precipitant: NaDDTC; filtration 0.4 μm, precipitant: NaDDTC; filtration 0.4 μm	not given	ENV	82
	Lake water		2.6 ± 0.5		2600
	Tap water		1.51		1510
	Spring water		2.31		2310				EDXRF
Pearl River Delta Economic Zone, CN:				ppb			not mentioned	“upper part of the clean water in the sample bottle” analysed	ICP-MS	not given	ENV	83
	West River	4 samples	0.002–0.003		2–3
	East River	9 samples	0.001–0.024		1–24
	Pearl River Delta	14 samples	0.001–0.032		1–32
	North River	1 sample	0.018		18
	Shenzen River	1 sample	0.039		39
Tirupati, IN:				μg L^−1			5 mL HNO3 in 1 L	0.45 μm cellulose membrane filter (after acidification)	SPE: piperidene dithiocarbamate-coated Amberlite XAD-7 resin	1200	ANAL	47
	“Natural” water 1		2.0 ± 0.04 (n = 5)		2000
	“Natural” water 2		1.7 ± 0.08 (n = 5)		1700				ICP-MS
Allard River, CA		3 sites	0.01, 0.01, 0.01	nmol L^−1	2, 2, 2		“several drops of conc. HNO3”	0.45 μm filter cartridges	ICP-MS	2	ENV	84
Colombière River, CA		3 sites	0.01, 0.01, 0.02		2, 2, 4
Tap water			BDL	ng mL^−1			not mentioned	filtration mentioned (conditions not given)	HMDE-ASV using chromazorul-S as complexing agent + CWT	100	ANAL	85
River water			0.3		300
Takahashi River, Okayama, JP			2.08 ± 0.05 (n = 5)	pg mL^−1	2.08		not mentioned	not mentioned	Preconcentration: glycine-type chitosan resin	0.1	ANAL	48
									ICP-MS
Xuzhou, CN:				μg L^−1			2% (v/v) HNO3	0.45 μm filter	Preconcentration: retention of Bi complex with Bismuthiol I on a nylon fibre-packed microcolumn	2.8	ANAL	86
	River water		0.53 ± 0.03 (n = 5)		530
	Lake water		0.34 ± 0.02 (n = 5)		340
	Tap water		0.26 ± 0.02 (n = 5)		260				HG-AFS
Tap water 1			33.8 ± 9.8 (n = 4)	μg L^−1	33 800		not mentioned	not mentioned	Cloud point extraction (surfactant: Tween 80)	800	ANAL	87
Tap water 2			34.9 ± 8.6 (n = 4)		34 900
Mineral water 1			264 ± 43 (n = 4)		264 000
Mineral water 2			211 ± 19 (n = 4)		211 000				FAAS
Mineral water 3			235 ± 15 (n = 4)		235 000
Surface water, Yangzhong city, CN		28 samples	0.043 ± 0.180 (0.001–0.963)	μg L^−1	43		pH < 1	0.46 μm filter	HR-ICP-MS	not given	ENV	88

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4. Values quoted in books

Table 3 contains values of bismuth concentrations in seawater reported in books and reviews. As expected, these values inevitably reflect the dispersion discussed above. However, the crucial point here is that the way these values are usually quoted does not adequately reflect the tentative nature of current knowledge on the subject. Moreover, sometimes authors (i) do not quote the source, (ii) copy from secondary references and, too often, (iii) uncritically reproduce a few, old values. These practices should be avoided because they merely lead to the persistence in the scientific literature of values that may have been later corrected or been experimentally superseded. Nor is it acceptable to read in a 2004 publication that “Although Bi is not detectable in drinking water, soil solution, or river water, it is detectable in sea waters at low concentrations”.¹¹⁴ This text exactly reproduces a text in a previous edition of the book¹⁰²—at which time the statement was already incorrect.

Table 3 Seawater bismuth concentration values quoted in secondary sources. References are given in chronological order

System	Bi concentration	Source given	Ref.
Seawater	0.00002 mg L^−1	none	89,90
Seawater	0.02 μg L^−1	91	92
Seawater	1 × 10^−10 M = 2 × 10^−2 μg L^−1	13	93
Seawater	0.02 μg L^−1	none	94
Seawater	4 × 10^−5 ppb	Lee, personal communication	95
Surface seawater	≈0.2 pmol kg^−1	22	96
Surface observed concentrations in seawater	20 ng kg^−1	13	97
Predicted mean water concentration	10 ng kg^−1	13	97
Vertex IV, Hawaii	Profile: 11 values; 36 pg kg^−1 (surface)	22, 28	98
Surface waters Atlantic	0.25 pM	22	99
Surface waters Pacific	0.2 pM	26	99
Deep waters Pacific	0.02 pM	26	99
Deep-Pacific Ocean	2 × 10^−14 mol kg^−1	28	100
Seawater	0.0042 × 10^−12 g g^−1	99	101
Seawater	0.2 to 0.1 pmol L^−1 up to 1000 m, 0.015 pmol L^−1 at 3000 m depth	28,96	102
Seawater	4 × 10^−9 ppm	101	103
Seawater	2 × 10^−8 mg L^−1	none	104
Seawater	1.6 × 10^−15 mol L^−1	probably 105	106
Seawater	20 ng L^−1	107	108
Seawater	400 ptt	none	109
North Pacific Ocean	0.03 ng kg^−1	28	110
Ocean	0.05 μmol m^−3	97	111
North Pacific Ocean	0.03 ng kg^−1	111	113
Surface ocean water	20–40 ng L^−1	90	113
World ocean water	20 ng L^−1	112	113

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5. New analytical methods: a plea for the publication of methods that work

There are quite a number of methods available for the determination of bismuth at major and trace levels such as ICP spectrometry (including ICP-AES and ICP-MS); atomic spectrometric techniques, (i.e., ET-AAS, FAAS and HG-AAS); and voltammetry. However, the dispersion shown above in the values of bismuth in surface waters suggests that the determination of the concentration of this element at ‘natural’ concentrations has not yet been completely resolved. The development of new approaches is thus needed and welcome. For this reason, all the new methods published in a number of well-known analytical and environmental chemistry journals since 2000 until now, and intended to be applied to surface waters, have been revised. The journals included are: Analytical Chemistry, Analytical Chimica Acta, Talanta, Microchemical Journal, International Journal of Analytical Environmental Chemistry, Journal of Analytical Atomic Spectroscopy, Analytical Bioanalytical Chemistry, Analytical Letters. Surprisingly, most of the methods published these last years (Table 4) have limits of detection well above the ones required for the methods to be applied to seawater and probably to most freshwater samples. Too often the authors ‘solve’ the problem by either stating that “tested water samples were found to be free from Bi content”¹²⁴ and that “no bismuth was present in these samples”¹²⁶ or, even more frequently, by showing that their method works on spiked samples containing unrealistically high bismuth concentrations. The question that remains to be answered by the scientific community is why do methods that will never work for the intended application continue to be published.

Table 4 Examples of new analytical methods published after 2000 and applied to natural waters. References are given in alphabetical order

DL^a in ng L^−1	Method^b	Application^c	Ref.
a When the value in the original publication is not in ng L^−1, the original value and units are also given in brackets. b See corresponding list for meaning of abbreviations. c BDL = below detection limit.
200 000 (0.2 μg mL^−1)	β-correction spectrometry	Spiked river water	115
80 (0.08 ng mL^−1)	FI-HG-ICP-TOFMS	NIST 1643d: 14.26 μg L^−1	116
8500 (8.5 μg L^−1)	ETAAS with tungsten containing chemical modifiers	Spiked seawater; natural seawater: BDL	117
95 000 (0.095 ppm)	Optical sensor based on (2E,4E)-5-(2,4-dinitrophenyl amino)penta-2,4-dienal	Seawater, tap water, mineral water, river water: BDL	118
1800 (1.8 μg L^−1)	Co-precipitation with Cu(II)-9-phenyl-3-fluorone + ICP-MS	Lake water, two different tap waters: BDL	119
800 (0.8 ng mL^−1)	ASV (HMDE) using TPN as complexing agent	Tap water: see Table 2	80
800 (0.8 μg L^−1)	Cloud point extraction (surfactant: Tween 80) + FAAS	Tap and mineral water: see Table 2	87
2.7 (0.0027 ng mL^−1)	Trapping on resistively heated W coil + HG-AAS	Certified reference water: TMDW: 10.3 μg L^−1	120
25	HG, sequestration in graphite tubes, AAS	Brackish water: BDL	121
1200 (1.2 ng mL^−1)	ASV using fast red as complexing agent	Spiked samples; unspiked spring and tap water: BDL	122
104 (5 × 10^−10 mol L^−1)	ASV (CPE) using BPR as complexing agent	Tap and river water: see Table 2	75
4500 (4.5 ng mL^−1)	ASV (HMDE) using morin as complexing agent	Tap water: see Table 2	71
1200 (1.2 μg L^−1)	Fluorimetry of the complex formed by BiI4^− and crystal violet	Potable water: BDL	123
100 (0.10 ng mL^−1)	ASV (HMDE) using chromazorul-S as complexing agent + CWT	Tap water: BDL; river water: 0.3 ng mL^−1	85
not given	SPE: XAD-4-salen + GF-AAS	River water: see Table 2	77
167 (8 × 10^−10 mol L^−1)	Complexation with thiourea and Br^− in acidic media + retention on activated C + spectrophotometry	Only spiked samples because “tested water samples were found to be free from Bi content”	124
70	HG-ETAAS with U-treated graphite tube	Seawater: see Table 1	43
0.1 (0.1 pg mL^−1)	Absorption on glycine-type chitosan resin + ICP-MS	Seawater and freshwater: see Tables 1 and 2	48
0.06	Comparison of FI-ICP-MS and FI-ETV-ICP-MS	NRCC CASS-3 and NASS-4: BDL	125
900 and 1200 (0.9 and 1.2 μg L^−1)	SPE: sodium DEDTC or piperidene dithiocarbamate-coated Amberlite XAD-7 resin + ICP-MS	“Natural” and seawater: see Tables 1 and 2	47
900 (0.9 ng mL^−1)	On-line preconcentration: chitosan resin functionalized with CCTS-DHBA + ICP-AES	NRCC SLRS-4 and CASS-4, river and seawater: BDL	49
		Off-line: see Table 2
20 (0.02 ng mL^−1)	Cloud point extraction (surfactant: Triton X-114, complexing agent: ditizone) + ET-AAS	Tap water: see Table 2	78
140 (0.14 ng mL^−1)	SPE: amberlite XAD-2 modified with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol + DP-ASV	Only spiked samples because “no bismuth was present in these samples”	126
500 (0.5 μg L^−1)	SPE: silica gel modified with 3-aminopropyltriethoxysilane + GF-AAS	Seawater: see Table 1	44
800 (0.8 μg L^−1)	SPE: Chromosorb-107 with and without APDC + GF-AAS	CRM-SW: BDL; seawater: see Table 1	45
31.0 ng L^−1	Preconcentration: sorption onto 8-hydroxyquinoline immobilized polyacrylonitrile hollow fibre membrane + ICP-MS	Seawater: see Table 1 (they measure values lower than the DL)	41
2.8 ng L^−1	Preconcentration: retention of Bi complex with Bismuthiol I on a nylon fibre-packed microcolumn + HG-AAS	Freshwater: see Table 2	86
2 (0.002 μg L^−1)	Tandem preconcentration by chelating resin adsorption (Chelex 100) and La co-precipitation + ICP-MS	NASS-4 open seawater, Ise Bay: BDL	42
0.03 (0.00003 μg L^−1)	Preconcentration by chelating resin adsorption (Chelex 100) + ICP-MS	NASS-4 open seawater: BDL; Ise Bay: see Table 1 (less than 50% recovery)	42
10 (0.01 ng mL^−1)	Octadecyl bonded silica cartridge modified with cyanex 301 + GF-AAS	Only spiked samples	127
0.05 (0.00005 μg L^−1)	Tandem preconcentration using a chelating resin (Chelex 100) + ICP-MS	CASS-4 seawater: BDL; Ise Bay: see Table 1	46

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6. Can current knowledge of bismuth solution chemistry help?

Even if the chemistry of bismuth has probably been less extensively studied than the chemistry of the other elements of group 15, it is relatively well-known. In recent years some aspects, in particular in relation to the use of bismuth in the semiconductor industry, have been thoroughly investigated. Bismuth chemistry is particularly rich because the coordination number of Bi(III) is highly variable (from 3 to 10) and its coordination geometry is often irregular, thus leading to the formation of a wide variety of compounds. However, as is often the case for many elements, most studies have been performed on solid phases or on solutions at concentrations many orders of magnitude higher than those found in natural waters. This is particularly important in the case of bismuth because Bi³⁺ is strongly acidic in water and has a strong tendency to form stable hydroxo- and oxo-bridged clusters whose extent of formation is strongly concentration dependent. Moreover, it is important to point out that what textbooks on inorganic chemistry often call ‘diluted’ (e.g., “On dilution, basic salts precipitate”¹²⁸) is still extremely concentrated compared to concentrations in natural waters.

The actual speciation of bismuth in natural waters does not seem to be well established. To illustrate this point, Table 5 gathers information published on bismuth speciation in seawater. All these results are, in principle, based on thermodynamic calculations but the constants used for these calculations are rarely given and their validity does not seem to have ever been systematically evaluated. On the contrary, Table 5 shows that most of the authors simply copy statements from previous publications that, in turn, cite previous ones. When the thread is tracked back to the initial sources, there appear to be very few of them and, at least in one case, the original is an old publication in Russian which most of the authors are unlikely to have read. After a long search, I have had access to the original publication (original text translated as a footnote in Table 5) and, amazingly, the set of suggested species does not seem to be based on any thermodynamic calculation. Moreover, it even contains an error in one species (BiCl⁻) that was reproduced in a well-known reference work¹³⁰ and, again, in a very recent book.¹¹³ As mentioned for total concentration values, superseded distributions remain in the literature without any apparent scientific reason.

Table 5 Suggested Bi speciation distributions in seawater. References are given in chronological order

Species	Source given	Ref.
a Because of the difficulties in accessing the original source, the translation of the original text is given: “Bismuth. According to the data of I. and W. Noddack,^12 in the water of the Gullmar Fjord the concentration of Bi is 2 × 10^−8%. This is the only determination of Bi in sea water. Soluble salts are BiO^1+ (perhaps BiOCl, BiCl^1−) and the most insoluble salt is BiOCl”.) and the most insoluble salt is BiOCl”. b Question mark in the original publication.
soluble: BiO^+ (perhaps BiOCl, BiCl^−), insoluble: BiOCl^a	no reference	129
BiO^+, BiCl^−, BiOCl, BiOCl	129	130
BiO^+, Bi(OH)2^+	no reference	93
BiO^+, Bi(OH)2^+, Bi6(OH)12^6+?^b	129, cited in 130	131
BiO^+, Bi(OH)2^+	no reference	132
100% complexed to OH (no species given)	original calculation (no equilibrium constant values given)	105
BiO^+, Bi(OH)2^+	105,132	96
Bi(OH)3^0	133	101
BiO^+, Bi(OH)2^+	no reference	104
Bi(OH)3^0	134	135
BiO^+, Bi(OH)2^+	96	135
BiO^+, Bi(OH)2^+	96	136
Bi(OH)3^0	no reference	106
BiCl4^−	137	108
Bi(OH)2^+, Bi(OH)3^0, Bi(OH)4^−	original calculation (pKs = 4.86, 12.7)	138
Bi(OH)3^0	no reference	139
BiO^+, Bi(OH)2^+, Bi(OH)3^0	no reference	140
BiO^+, Bi(OH)2^+	96	141
BiO^+, BiCl^−, BiOCl, BiOCl	131	113

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The situation is no better when so-called heterogeneous complexants (e.g., natural organic matter, metal oxides, aluminosilicates) are considered. To our knowledge, no laboratory study exists where complexation/sorption of bismuth by these complexants has been quantified. Dzombak and Morel, in their classic book on surface complexation modelling of hydrous ferric oxide binding,¹⁴² did not mention any binding value for bismuth. Nor did they venture to estimate it from LFER's (Linear Free Energy Regression) as they did for other elements for which experimental data were also missing (e.g., antimony, molybdenum, selenium). However, there are many reasons to think that bismuth binding by heterogeneous complexants is far from negligible, namely: (i) significant amounts of bismuth have been found associated to ‘particulate’ phases in natural waters (Tables 1 and 2); (ii) the few seawater profiles measured to date^22,28 clearly show non-conservative behaviour, with removal in upper waters and regeneration from suspended particles to solution roughly associated with the oxygen minimum at 500, attributed by the authors to the dissolution of manganese oxides acting as a carrier phase; (iii) according to Pearson's HSAB (Hard Soft Acid-Base) theory, Bi(III) should be a broad-line or soft metal ion; (iv) in the frame of its medical applications, bismuth complexation by biomolecules such as metallothioneins and transferrin has been studied in detail,^143–145 and strong binding found. Finally, other applications point to significant complexation of Bi(III) by organic ligands, for instance the fact that the antibacterial properties of bismuth are greatly improved when bismuth is combined with certain lipophilic thiol compounds¹⁴⁶ which enhance not only the lipophilicity but also the solubility of bismuth, or the extended use of a parameter called BiAS (bismuth active substances) to measure the presence of non-ionic surfactants present in polluted waters.¹⁴⁷

Knowledge about methylated species of bismuth in environmental and biological media is very limited. In contrast to arsenic and antimony, no methylated bismuth species have ever been found in surface waters.¹⁴⁸

7. Conclusions

On the basis of what has been published so far, it is not possible to make a sound estimation of bismuth concentrations in seawater. Nor is it possible to identify a range of probable concentration values for freshwaters which are not heavily polluted. At least one of the reasons seems to be related to the low concentrations of the element in natural systems and the inadequacy of some of the analytical methods applied. The increased use of bismuth because of its ‘green’ reputation requires a better understanding of its environmental behaviour which in turn demands the establishment of the current concentration levels in surface waters, a deeper insight into bismuth behaviour in dilute conditions, and the study of bismuth interactions with natural heterogeneous complexants. Regrettably, the unsatisfactory situation concerning bismuth is not unique; our current understanding of the chemical elements’ environmental behaviour being based too often on redundant studies of a limited number of elements. Abbreviations

AAS	atomic absorption spectrometry
AES	atomic emission spectrometry
AFS	atomic fluorescence spectrometry
APDC	ammonium pyrolidine dithiocarbamate
ASV	anodic stripping voltammetry
BDL	below detection limit
BPR	bromopyrogallol red
CCTS	cross linked chitosan
CFF	cross flow filtration
CL	95% confidence limits
CME	chemically modified electrode
CPE	carbon paste electrode
CV	coefficient of variation
CWT	continuous wavelet transform
DEDTC	diethyldithiocarbamate
DHBA	3,4-dihydroxy benzoic acid
DCASV	direct current ASV
DL	detection limit
DPASV	differential pulse ASV
EDXRF	energy dispersive X-ray fluorescence
ETAAS	electrothermal AAS
ETV	electrothermal vaporization
FI	flow injection
F2H2Dz	1,2-di-(2-fluorophenyl)-3-mercaptoformazan
FAAS	flame atomic absorption spectrometry
FIA	flow injection analysis
GF	graphite furnace
GFAAS	graphite furnace AAS
HG	hydride generation
HMDE	hanging mercury drop electrode
HR	high resolution
ICP	inductively coupled plasma
INAA	instrumental neutron activation analysis
MCGE	mercury-coated graphite electrode
MS	mass spectrometry
N	number of samples
NaDDTC	sodium diethydithiocarbamate
PSA	potentiometric stripping analysis
RDE	rotating disc electrode
RRDE	rotating ring-disc electrode
RSD	relative standard deviation
salen	N,N′′-bis(salicylidene)ethylenediamine
SFC	supercritical fluid chromatography
SPE	solid-phase extraction
SPM	solid suspended matter
SW-ASV	square wave ASV
TOFMS	time-of-flight mass spectrometry
TPN	thymolphthalexone
TXRF	total X-ray fluorescence spectrometry
UV	ultraviolet
VG	vapor generation

Acknowledgements

I would like to thank Wolfgang Hummel (PSI, Switzerland) for his perseverance in trying to find Vinogradov's classic book on oceanography and Dmitrii Kulik (PSI, Switzerland) for translating the section on Bi. I am particularly grateful to Pat Wilde for readily providing me with copies of two articles.

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Footnote

† Part of a themed issue dealing with water and water related issues.

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