Benjamin
Harris
and
Mohamed
Abou-Elwafa Abdallah
*
School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK. E-mail: M.abdallah@bham.ac.uk
First published on 21st April 2021
Surface riverine sediment samples were collected along the course of the River Medway, UK, between Yalding and the mouth of the estuary at 40 different sites. The samples were then analysed for hexabromocyclododecane (HBCDD) concentrations using a liquid chromatography system coupled to a high-resolution, accurate mass Orbitrap™ mass spectrometer. After normalisation to the sediment organic carbon (OC) content, average ΣHBCDD was 270 ng g−1 OC with a maximum concentration of 1006 ng g−1 OC. Spatial trend analysis revealed that industrial and residential land uses have significantly influenced HBCDD concentrations and profiles in riverine sediments. Higher concentrations of ΣHBCDD were found in sites near construction and maritime port locations, and these included freight ports, new builds and demolition sites. The HBCDD isomer profile reflected that of the commercial mixture with a comparatively high γ-HBCDD to α-HBCDD and β-HBCDD. The isomer profiles of sites located near construction activities indicate recent pollution events, with increased γ-HBCDD and decreased α-HBCDD compared to the study area's average profile. HBCDD isomer concentrations also indicated that the non-tidal portions of the river caused by locks showed a profile that was typical of older HBCDD contamination, indicating a possible sediment and HBCDD trap.
Environmental significanceHBCDD was detected in sediment samples collected along the course of the River Medway, UK, at varying levels, being higher in areas utilised for residential and industrial uses. Elevated levels of HBCDD around construction activities could be attributed to the possible use of HBCDD treated EPS and XPS for thermal insulation of buildings. This was also reflected in the average isomer profile of samples collected near construction areas, showing distinct similarities to the commercial mixture of HBCDD. Although the highest concentration recorded along the Medway was still not sufficient to pose imminent risk to human health, there is still an underlying risk of having such a toxic chemical in locally higher concentration spikes. The isomer profiles of samples in the non-tidal reaches of the Medway also suggested that locks acted as quite effective sediment traps, stopping the flow of HBCDD containing sediment along the river to the ocean. |
Due to its persistence, bioaccumulative and toxic (PBT) criteria, HBCDD was added to Annex XIV of the European REACH regulation and to Annex A of the Stockholm Convention on POPs. However, this includes a “specific exemption” for its use in EPS and XPS for thermal insulation of buildings. Technically HBCDD can still be produced, utilised, imported and exported until the 25th of December 2021, as long as it is for EPS and XPS or alternatively used for laboratory research.2,15 It is therefore still important to research and regulate the amount of HBCDD used globally.
Due to HBCDD treated products being classified as municipal waste rather than hazardous waste, it is treated with less precaution, often being sent to landfills and incinerators.16 Consequently, this leaves HBCDD vulnerable to leaching out of products in use or during waste disposal and eventually accumulates in the environment including rivers and water bodies.17 This is of importance given that marine environments contribute an estimated $21 trillion a year of human welfare to a global gross national product of $25 trillion. Despite coastal and shelf systems, such as the River Medway, contributing 60% of this, they are often viewed by industry as pollution sinks,18 and consequently POPs find their way into these water bodies and preferentially accumulate in their organic-rich sediments. Looking specifically at the region of the present study, the southeast of England is of major economic importance not just to the UK but also to wider Europe, with the EU declaring it “internationally-significant”, having the second largest economy of any region after London.19 Its construction industry specifically is expected to excel, with a predicted yearly growth of 2.2%, higher than that of the wider UK with 1.7% until 2021.20 Given the exemptions for use of HBCDD in XPS and EPS mentioned above, the potential for significant pollution events to occur due to the expected local growth of the construction sector should not be underestimated.
Previous research on HBCDD in a wide range of riverine sediment samples from across China found a general trend of an increasing concentration from the rural north to the heavily industrialised south east of China. The high concentrations (up to 206 ng g−1 dw) in the Yangtze River Delta, Pearl River Delta and southeast area of Fujian Province were linked to the fastest economic and industrial growth in the whole of China, contributing 33.5% of its GDP. These provinces are unsurprisingly therefore some of the highest polluters, accounting for 30.3% and 11.5% of municipal sewage and solid waste, respectively.21 Similar results were also recorded in the Weihe River Basin, showing a link between industrial areas, point source pollution and HBCDD concentrations,22 and other studies also confirmed that soil and sediment were the primary sink with γ-HBCDD being the primary isomer in that environmental compartment.3 In Europe, Suhring et al.23 measured HBCDD in surface sediment samples from the German rivers Elbe and Weser, the German Bight, Jadebusen, East Frisian Coast as well as the southeast coast of the UK. Sediment samples from the river Weser and East Frisian Coast show that HBCDD was not only present, but also reflect the isomer fingerprint of the commercial mixture, with up to 90% of HBCDD in the γ-isomer form. Comparatively, sediments from the southern UK coast contained up to 80% of the α-isomer. This was attributed to the abiotic conversion of γ-to α-HBCDD, enhanced under anaerobic conditions. This could indicate an older input of HBCDD to the UK coastal regions. This paper also suggests that HBCDD from the UK is being moved by ocean currents to the East Frisian Coast.23 Another study conducted in the UK found varying HBCDD concentrations in Thames river sediment that spiked at very specific points along the industrial areas of the river, with elevated levels of the γ-isomer, indicating the presence of recent pollution sources.24 This illustrates that despite the European and International restrictions on HBCDD, it continues to be a problem in our environment. With previous studies showing a link between industrial water courses and higher HBCDD concentrations, the need to monitor the River Medway becomes more apparent. This is further compounded by the UK Environment Agency admitting significant failures in recording POPs, specifically highlighting HBCDD25 being only monitored in water samples from 13 sites in Kent and the South of London.26
Against this backdrop, the present study aims to assess the concentrations of HBCDD main isomers in 40 riverine sediment samples collected along the River Medway, UK. Reasons for variability in concentrations and isomer profiles will be investigated to identify potential sources of HBCDD pollution (e.g. sewage outlets, industrial activities and construction sites) in this highly populated, industrial and economically important river, the Medway.
The sample collection campaign commenced on the 28th of May, 2019 and was completed on the 17th of June, 2019, lasting 3 weeks. One sediment sample was taken at each location shown in Fig. 1 (recorded using a GPS with ±4 m accuracy) and was accessed by foot. The sample area was divided into two segments by the M2 motorway bridge, between site 40 and site 8. This division represents the change in river use from rural and residential to industrial and a physical change from the upper to the lower course of the river. The riverbank length was measured for each segment and 20 sites distributed systematically along it. For the lower course, planned sample points were distributed every 3.87 km and for upper course every 3.12 km. Ease of access and private land ownership were taken into consideration.
At each location, one sample was taken by the insertion of a sediment corer into the surface sediment (5 cm depth) by foot as far into the river as was safely traversable. The sample was stored in a polyethylene sealable bag and kept in a freezer box until transported to the laboratories in Birmingham. Between sampling, the corer was cleaned using water, spray detergent and a brush so as to avoid cross contamination. At the University of Birmingham, the samples were freeze-dried, sieved through a 2 mm brass mesh and ground into a fine powder and then stored frozen in clean sealed polyethylene bags until extraction.
Concentration (ng g−1 OC) | α-HBCDD | β-HBCDD | γ-HBCDD | ΣHBCDD |
---|---|---|---|---|
Mean | 57 | 28 | 184 | 270 |
Median | 51 | 23 | 163 | 223 |
Minimum | 10 | 3 | 11 | 26 |
Maximum | 161 | 91 | 755 | 1006 |
Range | 151 | 87 | 743 | 980 |
Standard deviation | 37 | 21 | 168 | 218 |
Influenced (ΣHBCDD) | Not Influenced (ΣHBCDD) | |
---|---|---|
Construction | 453 | 182 |
Tidal | 309 | 149 |
Concentration (ng g−1 dw) | α-HBCDD | β-HBCDD | γ-HBCDD | ΣHBCDD |
---|---|---|---|---|
Mean | 1.8 | 0.9 | 6.3 | 9.1 |
Median | 1.4 | 0.6 | 3.8 | 5.8 |
Minimum | 0.3 | 0.1 | 0.3 | 0.7 |
Maximum | 6.3 | 3.5 | 29.4 | 39.1 |
Range | 6.0 | 3.4 | 29.1 | 38.4 |
Standard deviation | 1.5 | 0.9 | 6.9 | 9.1 |
Table 1 shows that the variability of the data collected is reasonably high throughout both TOC- normalized and unnormalized datasets. The low mean compared to the high range and standard deviation indicates that ΣHBCDD concentrations increased rapidly in a few selected cases. Table 1 also shows the mean ΣHBCDD of sites that could either be influenced by construction activities or tidal regions of the river, respectively.
High variability in ΣHBCDD is confirmed when the data is plotted on a distance concentration graph (Fig. 2). This was plotted from the furthest upstream sample site and ran along a distance measured transect through the middle of the river, plotting the corresponding concentrations of ΣHBCDD. The graph shows that there is considerable “noise” in the data corresponding to the industrial areas of the river. The residential area however is dominated by two identifiable peaks in concentration while the rural land use area has only one small peak in an otherwise flat line low concentration. Throughout the graph, the standout feature is the rapid increases and decreases in concentration illustrating the high range and standard deviation as shown in Table 1.
An ANOVA test conducted on log-transformed data confirmed that there were significant differences (P <0.05) in ΣHBCDD concentrations according to the land-use category as outlined in Fig. 2. A Tukey's post-hoc test revealed that the average ΣHBCDD in the rural stretch of the river was significantly lower than the measured average ΣHBCDD in residential and industrial areas of the River Medway.
A t-test was carried out to investigate the significance of ΣHBCDD concentrations between upper (sites 1–20) and lower (21–40) Medway course sample sites (Fig. 1). No significant difference was observed, which may be attributed to the absence of clear differences in physical features and impacts associated with different river course stages (e.g. tidal vs. non-tidal) between the upper and lower course sampling sites. However, another t-test revealed significantly higher ΣHBCDD concentrations in sites impacted by construction activities compared to that of the remaining sites. Further statistical analysis (One-way ANOVA and Tukey's posthoc test) was conducted on individual HBCDD isomer profiles to establish the “HBCDD fingerprint” and investigate the differences in HBCCD isomer distribution profiles between construction influenced and non-construction influenced sites (Fig. 3).
Fig. 3 Average HBCDD isomer profile in (a) construction influenced sites and (b) non-construction influenced sites (bar whiskers represent 1 standard deviation). |
Results revealed a significant difference in HBCDD isomer profiles. Specifically, higher contribution of γ-HBCDD, together with lower contribution of α-HBCDD, was observed in construction influenced sites. The observed HBCDD “fingerprint” in construction influenced sites (Fig. 3a) is more reflective of the isomer profile in HBCDD commercial formulations.5 In contrast, sites that were not impacted by construction activities (Fig. 3b) showed higher levels of α-HBCDD and lower levels of γ-HBCDD, while β-HBCDD levels showed no significant differences.
Another factor that may influence HBCDD levels in the sediment is the tidal nature of the river. Statistical analysis revealed significantly higher ΣHBCDD concentrations in tidal sites (Table 1), although no significant differences were observed between HBCDD isomer profiles in tidal and non-tidal sites (Fig. SI-1†).
However, this is not to say that there is no risk. The HBCDD concentrations in river Medwayare in line with, if not above, what the UK Government call a “source location” for HBCDD. In a report for the Department for Environment, Food & Rural Affairs (DEFRA), sites with a range of <0.1–30 μg kg−1 dw are considered source locations.31 Results gathered in this study show similar but slightly elevated levels of HBCDD. Due to the comparable range of concentrations, the River Medway would appear to show HBCDD levels that are typical of a source location in the UK. This is further backed up by other UK southeast based studies finding similar results. Ganci et al.24 found concentrations of HBCDD between <0.001 and 38 μg kg−1 dw in surface sediment samples from the river Thames. The greater range of ΣHBCDD concentrations in the Thames compared to the present study (Table 1) could be partly explained by the larger study area, and thereby the greater chance of a larger range of concentrations, albeit with a similar mean ΣHBCDD concentration (3.7 μg kg−1 dw).24 The Medway sediment displayed slightly higher, although broadly similar, concentration values. This is somewhat expected as the River Medway neighbours the river Thames, sharing a headland with much of the same industry and land uses. The higher HBCDD average in the present study could be attributed to the lower number of sites sampled compared to that of the Thames, allowing the few significant peaks in the residential section (Fig. 2) to increase the average. Overall, however, the two rivers show comparable levels of HBCDD, expected when both contain residential and industrial land uses along their respective banks.
The HBCDD concentration found in this study is not, however, similar to that in research conducted in the north of England. A study carried out by Morris et al.32 in the north of England and Scotland found concentrations ranging from <2.4–1680 μg kg−1 dw in surface sediments, the highest concentrations originating from the river Skerne. These are considerably higher than those recorded along the River Medway, which can be explained by the location of a BFR manufacturing plant in the neighbouring area. Despite this, other rivers in the north of England and Scotland such as the Tees, Tyne and Clyde showed concentrations up to 511, 322 and 187 μg kg−1 dw of HBCDD, respectively.32 This is in line with the results of Sühring et al., who reported higher HBCDD concentrations in surface sediment samples collected along the coast of northern England and Scotland compared to the English Channel and southern England.23 This may indicate a UK North/South divide in HBCDD concentrations, possibly due to the greater development and subsequent decline of industry in the north of England compared to the south,33 leaving many brownfield sites to slowly degrade or be demolished, which is a known source of HBCDD.34 Alternatively, this could be explained by the lower average temperatures the north of the UK experiences preventing re-dissolution of HBCDD and allowing its consequential build up in sediments. More research is needed in this area for proper conclusions to be drawn.
The general trend of increasing HBCDD concentrations in residential and industrial areas has also been observed in other parts of the UK and the world. Along the river Thames, HBCDD was found to increase where industrial activity was taking place.24 Further afield in Europe, HBCDD concentrations in riverine sediments showed similar trends on a greater geographical scale in varying industrialisation between the river Rhine and the river Meuse.32 In China, studies conducted by Li et al. also suggested that intensive industrialisation and urbanisation conspicuously increased HBCDD levels in surface sediments collected from seven major rivers.21
The concentrations of HBCDD in the industrial portions of the Medway decrease towards the estuary. This can be explained by the gradual inclusion and consequent influence of ocean currents that were absent in the other stages of the river. The influence of ocean currents could increase the rate at which HBCDD-contaminated sediment is removed from the site and dispersed into the open ocean resulting in lower concentrations.24,32 However,there are exceptions to this trend; Fig. 2 shows a spike in concentration at the last site sampled along the river, located at the mouth of the estuary next to the North Sea. This abnormal spike of HBCDD can be explained by two potential reasons. The first being the location of a port in Blue Town, a settlement near the sample point. The port predominantly deals with the transportation of goods through large container ships and is home to shipping companies such as SCA Logistics and Peel Ports London Medway. The spike in concentration would indicate that the port could act as a possible pollution source. This explanation is probable; HBCDD has had extensive use in the shipping industry to prevent fires at sea.2 Because cargo ships are old,35 they are likely to have experienced HBCDD use and their consequential presence and minor repair activities at port could account for the elevated HBCDD concentrations. The other possible reason is the location of a nearby Kent County Council recycling plant; there is evidence to suggest that recycling plants unintentionally release HBCDD into the natural environment36 and could offer an explanation to the observed peak.
The peak in concentration (408 ng g−1 OC) at site 18 (Fig. 1) is perhaps more unexpected, seen as the second to last peak in Fig. 2 next to the mouth of the estuary. This is unexpected as it goes against the trend of decreasing HBCDD close to the estuary mouth. Moreover, the land use that surrounds the site is predominantly rural, with no recent developments that could act as a pollution source. Due to its geographical location in a cove, it could be subjected to a low energy environment and therefore experience an increase in deposition and build-up of HBCDD contaminated sediment. Further investigation in the form of flow measurements and deposition rates would have to be undertaken to help explain this apparent anomaly.
The highest concentration of ΣHBCDD (636 ng g−1 OC) in the industrial segment of the river was recorded at site 4 (Fig. 1). Based on the current legislation surrounding the use of HBCDD, this has two probable explanations. Firstly, the development of the London Medway Commercial Park,37 where Amazon has recently built a warehouse. As previously stated, one of HBCDD's largest markets accounting for over 90% of HBCDD produced has been in XPS and EPS utilised in the construction industry.38 The construction of a large-scale commercial infrastructure project has the potential to use such materials in large quantities and thereby risk its unintentional release and leaching into the surrounding environment. Alternatively, the elevated HBCDD levels could also be attributed to the demolition of Kingsnorth power station. The power station was originally constructed in 1963,39 around the time that HBCDD appeared on the world market40 and has undergone a variety of renovations since, increasing the potential for HBCDD use. Its demolition could therefore have released quantities of HBCDD into the surrounding environment.
Other peaks in the industrial portion of the river include sites 11 (458 ng g−1 OC) and 12 (519 ng g−1 OC). These could be attributed to the construction of 1700 new homes and related infrastructure on St Marys Island,41 somewhere that XPS and EPS would potentially be used. Alternatively, the local port facilities for both pleasure cruising and industrial shipping located between the two sites (part of the aforementioned Peel Ports) could be a contributing factor. According to Peel Ports, their primary import materials are construction based.42 It is therefore likely that substantial amounts of flame-retarded materials such as XPS and EPS would have passed through or been stored at this port allowing for possible pollution events in the form of unintentional releases and the mishandling of goods.
Further upstream, the residential portion of the Medway is dominated by the highest concentration of HBCDD found in this study at site 22 (1006 ng g−1 OC). This spike can be explained by the ongoing housing developments of Peters Village based along the banks of the river. The use of XPS and EPS in the construction of Peters village in large quantities is likely, as a whole village is being constructed from scratch. What is alarming however is that an SSSI (Site of Special Scientific Interest) nature reserve is located next to the village.43 Considering HBCDD's toxicity and bioaccumulation potential,12,13 this may present some threat to wildlife and the surrounding ecosystems. Similarly, the potential implications of such high HBCDD concentrations for human exposure should be considered. A local primary school was built as part of the village plan.44 Not only are children more at risk to the potential adverse effects of HBCDD due to their lower body mass,45 but research has also shown that classrooms and schools form a major exposure pathway for HBCDD in UK children.46 While the elevated HBCDD concentration in the case of Peters Village remains well below the Canadian limit of 1.6 mg kg−1,30 careful monitoring of HBCDD is required in this area to avoid any potential health risk to the younger inhabitants of the village.
The construction industry would appear to play a large part in the elevation of HBCDD levels throughout the course of the river Medway (Table 1). This is hardly surprising given the fact that HBCDD is still in use in EPS and XPS, both utilised in the building process.2,7 Analysis showed that sample sites across all areas of the Medway that were located near to a construction site had statistically significant (P <0.05) elevated HBCDD concentrations compared to those that were not (Table 1). Further examination of their isomer profiles revealed statistically significant differences. Sites that were located near to known construction/demolition sites had levels that were more in line with the commercial mixture than those that were not (Fig. 3). The levels of γ-HBCDD increased by 14% in construction-impacted sites, while their α-HBCDD decreased by 12% on average and β-HBCDD decreased by 2%. The marked difference in isomer profiles could suggest a fresh pollution input of HBCDD to the sediments sampled at sites located near construction activities. This is evidenced by the HBCDD isomer profile similar to the commercial formulation with predominance of γ-HBCDD, which didn't have sufficient time to reach the expected α-HBCDD dominated equilibrium in the environment via isomerisation and faster degradation of the γ-isomer compared to α-HBCDD.47 These findings support the idea that construction activities can be a source of environmental pollution with HBCDD. Similar results were recorded in surface sediments along the Thames; although their construction influenced sites showed a stronger trend of increased γ-HBCDD and decreased α-HBCDD compared to those of the non-influenced sites.24 This suggests that the Thames may have experienced a greater number of recent pollution events than the Medway.
Our results of higher HBCDD levels linked to construction activities raise concern over how to proceed in terms of reducing the impact construction has in the short term until the end of HBCDD use in this sector in 2021.2 In addition to the use of “safe” alternatives when available, one possible solution would be to prioritise the use of XPS over EPS. The primary reason being that in the construction industry, HBCDD is generally used in much lower amount in XPS than in EPS,49 and therefore can be the lesser of two evils. It's recycling and future use is also important to consider as this is likely to extend past 2021. Research has shown that recycled EPS contains significantly higher levels of HBCDD in products than those made from recycled XPS,50 supporting the notion of prioritising the use of XPS over EPS.
Despite the possible actions taken to reduce HBCDD, its future concentrations in the environment are still predicted to increase by organisations such as DEFRA. The majority of buildings currently being demolished or refurbished have been constructed before the widespread use of HBCDD in the UK, while those constructed during widespread use are predicted to become HBCDD emission sources when they are demolished or renovated in the future.31 Ultimately more control over how HBCDD-containing products are handled during demolition and renovation are required to stop its release into the environment in light of its expected increase in concentrations.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1em00102g |
This journal is © The Royal Society of Chemistry 2021 |