Estimating fatty alcohol contributions to the environment from laundry and personal care products using a market forensics approach

Abstract

Fatty alcohol-based surfactants are widely used in detergents and personal care products; they are typically disposed of down-the-drain and are degraded or removed during wastewater treatment. Analytical data had shown concentration and profile differences between regions of the United States. Market sales data were purchased relevant to the sampling dates. In combination with analysis of the fatty alcohol profiles in the top selling products, the influent profiles were reconstructed and compared to the whole U.S. sales data. The per capita usage rate for fatty alcohols through these 4000+ top selling products was 4.9 g per day, with 88% arising from liquid laundry detergents and hand dish detergents. This extrapolates to a national usage of 185 000 tonnes per year. There were significant differences in the purchasing habits of the inhabitants across the four regions sampled, although this had minimal impact on the fatty alcohol profile which was dominated by the C₁₂ moiety. The U.S. market was also dominated by petrochemically-sourced chemicals. This market forensics approach using purchased sales data was able to extend our knowledge of the fate of these chemicals without a major (expensive) sampling and analytical campaign.

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Environmental impact

Fatty alcohol-based detergents include major surfactant classes used in a wide range of personal care products and detergents. These anthropogenic materials are disposed of down-the-drain, and enter wastewater treatment plants where they are degraded into materials that resemble naturally-occurring chemicals produced by plants and bacteria. This study used sales data pertinent to the regions where influent samples were collected from 24 wastewater treatment facilities in the United States. The sales data indicates very little difference in purchasing habits with regard to products although there are differences in how many of these products are used daily. Together with fatty alcohol profiles for faecal matter, the net contribution that the anthropogenic compounds make to the influent is calculated. These values range between 15 and 75% of the total fatty alcohol inventory. The data shows that 185 000 tonnes of fatty alcohols enter the drains each year in the United States, although the vast majority of these are degraded in the wastewater treatment plants and do not enter the receiving waters.

Introduction

Fatty alcohols with a chain length between C₁₀ and C₁₈ are the most common ingredients of several detergents and personal care products (PCPs); they are typically used in the form of alcohol ethoxylates (AE), ethoxysulphates (AES) or sulphates (AS).¹ A smaller quantity are used as free fatty alcohols.^2,3 Typical products that contain these compounds include liquid hand soaps, liquid and powdered laundry detergents, hand dishwashing liquids, shampoos and deodorants. A study of these and other products⁴ indicated that some products that were expected to contain fatty alcohols, such as fabric conditioners, did not at the time of sampling. Similarly, some particular product brands switch between olefin sulphonates and alcohols depending on market conditions. The fatty alcohols as ethoxylates and sulphates may constitute between 3% and 30% of the final product formulation (http://www.scienceinthebox.com) in the UK; it is assumed that product formulations will be similar in the United States and other markets. The use and application of these products leads to their down-the-drain disposal and subsequent treatment in a wastewater treatment plant (WWTP). Previous work has identified the fatty alcohol compounds without ethoxylation or sulphation as the greatest contributor to the ecological risk.⁵

Fatty alcohols are also naturally produced by all living organisms⁶ and the aqueous environment typically contains long-chain primary fatty alcohols (>C₂₀) from terrestrial plants, C₁₄ and C₁₆ from unicellular algal synthesis and a series of branched and odd-chain compounds (C₁₃–C₁₉) from bacterial biomass. In the investigation of one clearly defined river catchment at Luray, Virginia,⁷ 84% of the fatty alcohols in the river sediments downstream of the WWTP discharge point were derived from terrestrial plants with 15% coming from in situ production by algae. The remaining 1% was ascribed to bacterial fatty alcohols from both in situ production and WWTP effluents.

Previous investigations^7,8 have shown that the fatty alcohols derived from surfactants have characteristic stable isotopic signatures and can be distinguished from natural materials. Most fatty alcohols used in formulations are synthesised from petrochemical sources with only a small quantity in the U.S. market³ derived from palm oils and other oleochemical sources. In some markets such as Japan, a larger proportion of the source fatty alcohols are derived from palm products.² Environmental studies have shown that the fatty alcohols entering the WWTPs are rapidly removed through degradation and sorption to biosolids, and the liquid effluents contain only fatty alcohols derived from bacterial synthesis within the WWTPs. This has allowed the risk associated with the disposal of these compounds to be assessed.⁹

As part of a study in the United States across three eco-regions and several different secondary treatment types,¹⁰ significant differences could be seen in the fatty alcohol profiles of the influents. The influent inventory is composed of faecal matter and food waste as well as surfactants in PCPs and detergents. At the time of reporting it was not possible to determine whether the differences seen between the eco-regions were due to the purchasing habits of the people in the catchment. Data were subsequently obtained from IRI (Information Resources, Inc., http://www.iriworldwide.com/) on the products sold in the 24 weeks prior to the sampling in each of four areas in order to characterize the contribution of consumer products to the load of fatty alcohols in the influent of WWTPs using a market forensics approach.⁴ The sales data for the whole U.S. market were also obtained to allow extrapolation to the national scale.

Materials and methods

Data on the purchasing habits of residents in the each of the four eco-regions studied were purchased from IRI. Data had previously been purchased for the Luray catchment,⁴ part of the Roanoke region, although at that time (2009) the sales in Wal-Mart stores were unavailable. Since August 2012, these data have become available retrospectively. Data for the entire state of Oklahoma were used to represent the samples collected across the central and north central portion of the state; for Ohio, data for the Cleveland market region was used; for Oregon, data for the Portland market region were used; and for Luray, Virginia, data for the Roanoke market region were used. As well as these regional sales areas, the whole U.S. market was used to allow comparison between each region and the national habits and to determine the national fatty alcohol contributions to the sewer systems.

The fatty alcohol influent profiles and stable isotope results were taken from the study of 24 different WWTPs, eight in each of Oklahoma, Ohio and Oregon;¹⁰ the data for Luray was taken from Mudge et al.⁷ Population data for each WWTP catchment was taken from the 2010 census conducted by the U.S. government (http://www.census.gov/2010census/) and the population for the market sales regions came from the metadata supplied by IRI. The population for the whole of the United States was assumed to be 311 million based on expected growth from the 2010 census.

Using the sales data from the 2009 study in Luray, Virginia, 34 products had been purchased in local stores and analysed for their fatty alcohol profiles. The compounds were analysed as their alkyl iodides and the methods used can be seen in Mudge et al.⁷ The product types included in the market sales and sampling included liquid laundry detergents (LLD), hand dish detergents (HDD), powdered laundry detergents (PLD), liquid hand soaps (LHS), deodorants (DEO), shampoos (SHA), automatic dish detergents (ADD) and liquid fabric softeners (LFS). The latter two classes, however, had no fatty alcohols present at the time of analysis.

Results and discussion

A summary of the parameters associated with the sales regions can be seen in Table 1. The regions in the marketing surveys have populations between 1.2 and 3.8 million people and represent between 0.4 and 1.2% of the total U.S. population.

Table 1 Summary statistics for sales of selected product classes in each region and nationally across the United States

Market area	State	Population	Population (percentage of United States)	Mean daily usage rate of products (tonnes per day)	Usage relative to U.S. total (%)	Usage relative to population (%)	Per capita usage rate (g per day)
Roanoke	VA	2 291 845	0.74	90	0.40	54.17	39.2
Oklahoma	OK	3 814 820	1.23	141	0.62	50.94	36.8
Cleveland	OH	2 075 531	0.67	62	0.28	41.38	29.9
Portland	OR	3 182 474	1.02	64	0.28	27.61	20.0
United States		311 000 000	100	10 354	100	100	33.3

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The mean daily usage of all products (4000+) surveyed amounted to 10 354 tonnes per day across the whole of the United States. Within the different market areas, the usage was between 0.28% of the U.S. total for the Portland market to 0.62% for Oklahoma. The ratio of the usage relative to the population expressed as a percentage shows that the Portland market is using only 27% of what might be expected given the national usage rate while the Roanoke market is using 54% of the average. This is reflected in the per capita usage rate which ranged from 20 g per day in Portland to 39.2 g per day in the Roanoke market. The mean rate is 21.9 g per day.

Of the total market for compounds that contain fatty alcohols, the 34 purchased and analysed made up between 69.4% and 74% of the total product sales. The breakdown with respect to the product classes can be seen in Table 2. For example, a single shampoo product with its flanking brands (different “flavours” of the same-based product) was purchased and collectively comprised 27.2% of the total shampoo sales across the United States.

Table 2 The per capita daily usage of each sampled product within the four regions and for the whole United States^a

a Note: the differences shown are for product usage in each sampling region compared to the U.S. purchasing habits. Cells highlighted in red use less of those products compared to the national average, while those in green use more.

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The data in Table 2 clearly show which anonymous products make the greatest contribution to the daily usage. LLD 8 is the biggest single seller for these products and the LLD class of products is also the largest contributor to the wastewater system. Relative to the national sales for these products, the range in the regions varied from −14.7% to +10.2%; this reflects the local purchasing habits of the inhabitants of each region. For instance, the private label LHS were 8% above the national average in Oklahoma but the same soaps were 10% below the national average in Oregon. However, this Oregon bias against private label products for LHS was not repeated for the HDD where the private label products outsold the national average by over 5%.

Since the product usage data are averaged over the whole of the sampled region, there are no differences in the profiles between individual WWTPs within that region. By using the fatty alcohol composition for each product type, and using the profiles determine through analysis,⁴ the amount of each fatty alcohol entering the wastewater system can be determined. The profiles for each region can be seen in Fig. 1. The differences between eco-regions are small and there is little difference between each eco-region and the United States as a whole. The profile is dominated by the C₁₂ fatty alcohol with smaller amounts of C₁₃, C₁₄ and C₁₅. The most abundant naturally-occurring, short-chain fatty alcohol in the environment, the C₁₆, and other chain lengths make small overall contributions. This profile is typical of petrochemical sources as the odd chain length compounds make a small contribution to the natural synthesis. The C₁₂ is boosted by the high contribution from products manufactured from palm oil.

Fig. 1 The reconstructed fatty alcohol profiles based on sales of “down-the-drain” products in each catchment and the United States.

The branched chain compounds, normally associated with bacterial synthesis in the environment, make up approximately 10% of the total profile.

The fatty alcohol contribution is dependent upon both the product sales and the fatty alcohol concentration in each product. The fatty alcohol concentrations (as ethoxylates, sulphates and ethoxysulphates) in the products ranged from about 3% of the total in powdered laundry detergents to 30% in the shampoo. The contribution that the product types make to the total fatty alcohol inventory can be seen in Table 3. In the case of the shampoo sample, although it comprises 27.2% of the total sales, it only contributes 6.9% of the total anthropogenic fatty alcohol contribution to the WWTP influents.

Table 3 The number of products analysed, their contribution to the total market and their anthropogenic fatty alcohol contribution to the WWTP influent by region^a

Product type	Number of analysed products	% of U.S. market for specific product type	% Fatty alcohol contribution to the products in the influent
			VA	OR	OH	OK	USA
a Note: the number of analysed products is less than the 34 actually investigated as nine had no fatty alcohols present at the time of analysis; none of the fabric softeners contained fatty alcohols nor did the automatic dish detergents.
SHA	1	27.2	6.7	7.5	5.6	7.4	6.9
DEO	2	27.9	0.6	0.8	0.7	0.7	0.7
LHS	4	91.3	2.1	3.0	2.8	2.5	2.5
LLD	10	85.6	63.7	66.6	63.4	64.4	63.3
PLD	3	53.6	2.9	2.0	1.5	2.4	1.9
HDD	5	83.6	24.1	20.2	26.0	22.7	24.7
Per capita daily fatty alcohol usage (g per day)			4.05	1.93	3.18	3.75	3.45

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The LLD are the major contributors of fatty alcohols to the sewer with around 63% of the total, followed by the HDD with around 25%. These two product classes make up ∼88% of all fatty alcohols disposed of down the drain across the U.S. There are only minor differences across the different regions.

The measured fatty alcohol profiles in the WWTP influents across the 24 sites were significantly different,¹⁰ although there were more similarities between the eco-regions than between WWTP type. This can be seen through the groupings in the principal component analysis (PCA) using normalised fatty alcohol profiles in each of the influent samples (Fig. 3 in ref. 10). The sampling sites aggregated according to their region with the Ohio samples relatively enriched in the C₁₂ fatty alcohol, while longer-chain compounds make up a higher proportion in the other two eco-regions. The measured influent profiles in the four eco-regions (Fig. 2) are the sum of several sources and processes:

Fig. 2 The mean profile of the fatty alcohols in the influent of the WWTP by eco-region (state).

(1) Faecal matter from residents of the WWTP catchment which may be partially dependent on the dietary habits of the people.

(2) Food waste, again related to the dietary habits. It is anticipated that this fraction would be relatively enriched in the long-chain fatty alcohols derived from terrestrial plants.

(3) Terrestrial plant matter washed into the drains in combined systems.

(4) Detergent and PCP usage.

(5) Non-domestic contributions, although the aim was to minimise this as much as possible during the selection of the appropriate WWTPs for sampling.

(6) In-pipe biotic and abiotic degradation processes between the points of entry into the sewer and influent sampling point.

The food waste is expected to be a small contributor and relatively few long-chain fatty alcohols were measured in the influents, also eliminating surface water inputs. The non-domestic contributions were designed to be low (<10%) through selection of the WWTPs prior to sampling.¹⁰ Therefore, the majority of the differences would be related to the dietary habits of the residents and their surfactant usage. A simple minimisation of the sums of squares algorithm was used to mix the two source profiles together for each WWTP/eco-region and assess the magnitude of the differences to the measured influent profile. The results were varied and three examples can be seen in Fig. 3.

Fig. 3 The residual sums of squares for the differences between calculated mixtures of faecal fatty alcohols and consumer products with actual influent profiles. The minima (best fits) are indicated.

The example from Del City (Oklahoma) had a minimum sum of squares at 53% and the size of the residual squares was small indicating a relatively good fit to the measured profile. The catchment of Del City, a suburb of Oklahoma City, is relatively small with short pipe lengths to the WWTP, a sequencing batch reactor (SBR). Therefore, the faecal matter profile taken from a UK study together with the eco-region mean product usage profiles are able to adequately explain the influent profile. In the case of Luray (Virginia), a smaller percentage of the influent is from detergent usage (27%) which compares well with the data previously published (25%) before the Wal-Mart sales data were available.^4,7 The residual sum of squares at the minimum point is significantly greater than the values for Del City indicating other sources or processes have an effect on the influent. Inspection of the influent profiles shows that the C₁₈, a fatty alcohol with a small abundance in either faecal matter or consumer products, is present in relatively high amounts (Fig. 2). This may arise from in-pipe processes as the pipe runs are longer in this catchment. The same is likely to be true for the Massillon (Ohio) catchment, although at this location the detergents and PCPs make a greater contribution to the influent (75%).

Individual WWTPs had different strategies to balance the flows through the plant from the influent; the lagoonal systems tended to have a large capacity and all of the flow was directed through the works, although the residence time would be dependent upon the rainfall. Balancing tanks were present in many works to ensure a constant flow through the subsequent stages. The SBRs would begin their processing after having been filled, although flows that overwhelmed this capacity may have been directly discharged through combined sewer overflows.

The individual contributions to the influents from the surfactant component can be seen for each WWTP in Table 4. The average percentage surfactant present in the influent, based on the best fit of the faecal and product profiles, was ∼26% in the Oregon and Virginia catchments studied and about 50% in the Ohio and Oklahoma catchments. This may be explained simply by the amount of consumer products used in the different regions; the per capita usage rates for the products was least in Oregon and greatest in Virginia (Table 3). The data clearly show significantly greater variability in the fatty alcohol profiles of the influents within the same region, compared to the profile of the products between regions. The influent data from Oregon is the most internally consistent in terms of the proportions; the Oregon C₁₈ ranges from 31.9% to 47.4%, while the range in Ohio is 6.8–55%.

Table 4 The fatty alcohol composition (proportion) of the composite influent samples from each WWTP^a

Sample	WWTP	% Consumer products	C11	BrC12	C12	BrC13	C13	BrC14	C14	C15	C16	C17	C18	C20
a Note: the % consumer products is the best fit to the minimised sum of squares; an X in this column indicates no valid solution in this catchment. The fatty alcohol profiles for the products used in each region (Fig. 1) are also shown. The WWTP biological stage technology is also indicated: Lag = lagoon, Oxi = oxidation ditch, SBR = sequencing batch reactor, Act = activated sludge, TBF = tricking bed filter, RBC = rotating biological contactor.
Oregon	Products		0.016	0.041	0.343	0.041	0.200	0.012	0.193	0.138	0.004	0.010	0.003	0.000
Astoria	Lag	38			0.171		0.028		0.083	0.055	0.298		0.330	0.005
McMinnville	Oxi	27			0.100		0.020		0.050	0.041	0.323		0.421	0.009
Stayton	SBR	25			0.117		0.012		0.048	0.034	0.351		0.421	0.004
Silverton	Act	19			0.052		0.014		0.053	0.039	0.353		0.474	0.012
Molalla	Lag	23			0.092		0.012		0.069	0.033	0.363		0.399	0.010
Everett	TBF & Lag	31			0.113		0.025		0.090	0.053	0.311		0.319	0.006
Chehalis	SBR	24			0.068		0.022		0.076	0.059	0.332		0.394	0.006
Corvallis	Act	22			0.064		0.014		0.055	0.034	0.332		0.425	0.019
MEAN		26.1
Ohio	Products		0.016	0.040	0.346	0.039	0.203	0.013	0.193	0.135	0.003	0.008	0.004	0.000
East Liverpool	RBC	51			0.009	0.003	0.000		0.009	0.011	0.064	0.798	0.106	0.001
Alliance	Act	X			0.770	0.000	0.000		0.000	0.000	0.000	0.000	0.230	0.000
Massillon	Oxi & TBF	75			0.421	0.000	0.000		0.055	0.000	0.104	0.000	0.420	0.000
Fish Creek	Oxi	44			0.028	0.001	0.000		0.012	0.105	0.097	0.544	0.211	0.001
Strongsville	RBC	48			0.139	0.000	0.000		0.147	0.000	0.164	0.000	0.550	0.000
French Creek	Act	15			0.137	0.015	0.000		0.000	0.000	0.469	0.035	0.345	0.000
Danville	Lag	X			0.697	0.035	0.000		0.103	0.012	0.085	0.000	0.068	0.000
New Bremen	Lag & TBF	65			0.415	0.000	0.000		0.077	0.000	0.232	0.000	0.277	0.000
MEAN		49.7
Oklahoma	Products		0.016	0.044	0.346	0.042	0.198	0.012	0.186	0.138	0.003	0.009	0.004	0.000
Winfield	Oxi	72			0.306	0.004	0.060		0.101	0.029	0.142	0.000	0.223	0.005
Stillwater	Act	47			0.146	0.002	0.030		0.107	0.054	0.185	0.005	0.405	0.023
Edmond	Oxi	36			0.015	0.007	0.082		0.160	0.044	0.237	0.000	0.419	0.011
Deer Creek	RBC & Act	49			0.194	0.004	0.044		0.117	0.044	0.240	0.000	0.331	0.009
Del City	SBR	53			0.176	0.006	0.075		0.213	0.088	0.245	0.004	0.192	0.001
Ada	SBR	45			0.143	0.003	0.043		0.115	0.053	0.218	0.006	0.369	0.018
Weatherford	Act	57			0.221	0.004	0.056		0.134	0.043	0.201	0.004	0.311	0.010
Elk City	Lag	47			0.165	0.009	0.034		0.065	0.030	0.204	0.010	0.293	0.009
MEAN		50.8
Virgina	Products		0.014	0.045	0.350	0.042	0.196	0.012	0.187	0.137	0.004	0.010	0.004	0.000
Luray	Oxi	27			0.035		0.011		0.034	0.028	0.170	0.012	0.313	0.012

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The per capita daily usage of fatty alcohol-based surfactants for the analysed products can be seen in Table 3. The national average is 3.45 g per day which can be extrapolated to 4.92 g per day for all 4000+ products in the survey. This is equivalent to 1533 tonnes per day nationally or 560 000 tonnes annually. This is about the same as the estimated apparent consumption for detergent alcohols in North America for 2012.³ However, the reported percentages in the products are for the ethoxylates, sulphates or ethoxysulphates derivatives rather than the parent fatty alcohol alone. Using a mean ethoxylate number of nine,¹¹ the average total surfactant molecular weight will be around 600 Daltons with approximately 200 Daltons arising from the fatty alcohol component. Therefore, only 33% of the surfactant in the product will be a fatty alcohol, which would bring the annual contribution down to 185 000 tonnes which compares to a value of 523 000 tonnes consumed in North America (includes Canada and Mexico) in 2012.³ In the DeLeo et al. paper,⁴ it was noted that there are other fatty alcohol-based surfactants used in formulated products that are not considered here and there are commercial uses of these surfactants (hotels and other commercial laundries, etc.) that were also not included. Gubler and Inoguchi⁴ state a further 7% of alcohol ethoxylates and alcohol ethoxysulphates are used in institutional and commercial cleaning products and industrial applications. Further discrepancies may partly arise from inaccurate percentage information of fatty alcohol content in the products.

These data show a per capita contribution of fatty alcohols from consumer products to the wastewater system of 4.92 g per day with 3.45 g of this coming from the 25 products analysed. A further 5–60 g of fatty alcohols arises from faecal material. Stable isotope analyses of samples taken from the influent in all 24 WWTPs^7,10 showed that the majority of the fatty alcohols used in the detergents and PCPs were derived from petrochemical sources with relatively few oleochemical primary sources. In some cases, the products that contained oleochemically-derived fatty alcohols were also marketed as such.²

The fatty alcohols in the influents were located in the two-dimensional stable isotope figure to indicate they were a mixture of faecal material and consumer products (Fig. 4). In this figure, the compound-specific stable isotopes (data from Mudge et al.¹⁰) define the location of each influent sample and the colour describes the percentage contribution that the surfactant component makes to the influent on the basis of the minimisation of the sum of squares for the profiles. The location of the faecal matter from the UK study is indicated together with the range of values for petrochemical- and oleochemical-based surfactants from the previous studies using purchased products and raw materials from the manufacturers.

Fig. 4 The influent samples composition based on their stable isotopic composition and surfactant alcohol contributions. The crosses indicate the mean projection. Data from Mudge et al.¹⁰

Based on their stable isotopic signature, the WWTP influents occupy a region between the faecal signature and the petrochemical-based detergents. Since the faecal signature came from analysis in the UK, it is possible that the U.S. appropriate values will occupy a larger region which may be more to the left on this figure depending on local diets. While not emphatic, there is some tendency for the influent samples with the highest consumer product loadings, based on the minimisation of the sum of squares method, to be closer towards the petrochemical signature. The influents did not tend towards the oleochemical signature which reflects the prevalence of petrochemical sources in the U.S. market.

Conclusions

The per capita usage rate of fatty alcohol-based surfactants across the United States is 4.92 g per day. There are differences across the eco-regions investigated here, which contribute between 57 and 122% of the national average. Although there are differences in the total usage across the regions, the products purchased showed relatively small differences and the LLD made the greatest contribution, followed by the HDD. These two product categories made up 88% of all the contributions from the classes investigated. If these data are extrapolated to the nation, around 185 000 tonnes of fatty alcohols will enter the WWTPs annually from formulated consumer products. This compares well to a consumption rate across North America of 523 000 tonnes,³ especially considering the extrapolation included most but not all fatty alcohol-based surfactants and consumer cleaning product applications. AE, AS, AES and free alcohols constitute 87% of the total detergent alcohol market volume; in addition, an estimated 2% of AE and AS/AES is used in other cleaning product applications, and 7% of AE and AES is used in institutional and commercial cleaning products and industrial application in North America.³ Canada may contribute around 10% of the total U.S. usage. This approach demonstrates the effectiveness of the market forensics approach to estimating loads of consumer product chemicals to WWTPs.

The fatty alcohol profiles of the products include the C₁₂ compound as the major component and 87% of the totals are comprised by the four compounds C₁₂, C₁₃, C₁₄ and C₁₅. The large amounts of the odd-chain length compounds confirm a petrochemical source for these surfactants. This source is also prevalent in the production and consumption data from the Chemical Economics Handbook.³ Oleochemical sources make a larger contribution outside of North America. The influent profiles in the 24 WWTPs are enriched in C₁₈, C₁₆ and C₁₂; by combining the fatty alcohol profiles of faecal matter and the products, the surfactants make up between 15 and 75% of the total influent inventory. Where the pipe runs to the WWTP are short, there are fewer in-pipe processes that appear to lead to the formation of C₁₈ in the samples.

Despite the daily usage rate of around 3450 tonnes of fatty alcohols (the 1/3^rd of the daily product usage that includes the ethoxylate/sulphate component), these compounds were not observed entering the environment through the WWTPs studied. This is due to their complete removal within the plants and the synthesis of new fatty alcohols by bacteria; the stable isotopes confirm this process.¹⁰

Notes and references

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2. R. F. Modler, Detergent Alcohols, SRI Consulting, 2007.
3. R. Gubler and Y. Inoguchi, Detergent Alcohols, 2013.
4. P. C. DeLeo, S. M. Mudge and S. D. Dyer, Environ. Forensics, 2011, 12, 349–356.
5. S. D. Dyer, H. Sanderson, S. W. Waite, R. Van Compernolle, B. Price, A. M. Nielsen, A. Evans, A. J. Decarvalho, D. J. Hooton and A. J. Sherren, Environ. Monit. Assess., 2006, 120, 45–63.
6. S. M. Mudge, S. E. Belanger and A. M. Nielsen, Fatty Alcohols – natural and anthropogenic sources, RSC, Cambridge, 2008.
7. S. M. Mudge, P. C. DeLeo and S. D. Dyer, Environ. Toxicol. Chem., 2012, 31, 1209–1222.
8. S. M. Mudge, W. Meier-Augenstein, C. Eadsforth and P. DeLeo, J. Environ. Monit., 2010, 12, 1846–1856.
9. H. Sanderson, R. Van Compernolle, S. D. Dyer, B. B. Price, A. M. Nielsen, M. A. Selby, D. Ferrer and K. Stanton, Sci. Total Environ., 2013, 463–464, 600–610.
10. S. M. Mudge, P. C. DeLeo and S. D. Dyer, Sci. Total Environ. DOI:10.1016/j.scitotenv.2013.09.078.
11. T. Wind, R. J. Stephenson, C. V. Eadsforth, A. Sherren and R. Toy, Ecotoxicol. Environ. Saf., 2006, 64, 42–60.

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