OR/18/052 Results from GC-MS and LC-MS datasets

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Lapworth, D J, Crane, E J, Stuart, M E, Talbot, J C, Besien, T, and Civil, W. 2018. Micro-organic contaminants in groundwater in England: summary results from the Environment Agency LC-MS and GC-MS screening data. British Geological Survey Internal Report, OR/18/052.

Top 50 GC-MS substances by frequency of detection[edit]

Data description[edit]

The top 50 substances from the GC-MS dataset selected by frequency of detection are shown in Figure 3.1. A statistical summary of the data is shown in Table 3.1. Figure 3.2 shows the distribution of the results for the 50 most frequently detected substances by GC-MS using box plots. Due to the low frequency of detections, the box plots highlight the outlier values for each substance rather than the interquartile range, which for all of these substances is below the detection limit and was not computed.

Figure 3.1    Bar chart of 50 most frequently detected substances by GC-MS screen (description of compound classes is given in Table 2.2).
Table 3.1    Summary statistics for 50 most frequently quantified substances in GC-MS screen. For all analytes the minimum concentration detected was below the LOD. The proportion of positive detections was too low to calculate a 5th percentile, median, mean or standard deviation. All concentrations are in units of µg/L.
Ranking CAS Number Analyte Short name Use code * LOD 95th percentile concentration Maximum concentration Number of analyses Number of positive detections % analyses with positive detections
G01 1912249 Atrazine Atrazine Pest 0.01 0.01 0.75 11368 1069 9.40
G02 79016 Trichloroethene TCE HSol 0.01 0.13 184 11368 948 8.34
G03 80057 Bisphenol A BPA Plast 0.01 0.09 100 11368 939 8.26
G04 106650 Butanedioic acid, dimethyl ester Dimethyl succinate PPCL 0.01 0.02 74 11368 769 6.76
G05 6190654 Atrazine-desethyl (Desethylatrazine) Desethyl-atrazine Pest 0.01 0.01 1 11368 728 6.40
G06 127184 Tetrachloroethene PCE HSol 0.01 0.14 180 11368 668 5.88
G07 134623 N, N-Diethyl-m-toluamide DEET PPCL 0.01 0.01 17 11368 666 5.86
G08 108941 Cyclohexanone Cyclohexanone Indu 0.01 0.04 300 11368 638 5.61
G09 206440 Fluoranthene Fluoranthene PAH 0.01 0.01 3.4 11368 622 5.47
G10 129000 Pyrene Pyrene PAH 0.01 0.01 2 11368 606 5.33
G11 122349 Simazine Simazine Pest 0.01 0.01 0.42 11368 538 4.73
G12 123911 1,4-Dioxane 1,4-dioxane Indu 0.01 0.01 63 11368 527 4.64
G13 58082 Caffeine Caffeine PPCL 0.01 0.01 1.8 11368 484 4.26
G14 117817 Bis(2-ethylhexyl) phthalate (DEHP) DEHP Plast 1 1 62 11368 452 3.98
G15 627930 Dimethyl adipate Dimethyl adipate Indu 0.01 0.01 150 11368 360 3.17
G16 75274 Bromodichloro
-methane
Bromodichloro
-methane
HSol 0.01 0.01 150 11368 344 3.03
G17 124481 Chlorodibromomethane Chlorodibromomethane HSol 0.01 0.01 180 11368 342 3.01
G18 115866 Triphenyl phosphate TPPA Indu 0.01 0.01 2 11368 331 2.91
G19 75252 Bromoform Bromoform HSol 0.01 0.01 96 11368 318 2.80
G20 2008584 2, 6-Dichlorobenzamide BAM Pest 0.01 0.01 70 11368 313 2.75
G21 3622842 Benzenesulfonamide, N-butyl- BBSA Plast 0.2 0.2 4000 11368 302 2.66
G22 119619 Benzophenone Benzophenone PPCL 0.01 0.01 0.8 11368 288 2.53
G23 108623 Metaldehyde Metaldehyde Pest 0.01 0.01 6.4 11368 280 2.46
G24 126863 2,4,7,9-Tetramethyl-5-decyne-4,7-diol TMDD Indu 0.03 0.03 6 11368 277 2.44
G25 87412 1(3H)-Isobenzofuranone 1(3H)-isobenzofuranone Indu 0.01 0.01 1.2 11368 246 2.16
G26 77732093 Oxadixyl Oxadixyl Pest 0.01 0.01 3 11368 234 2.06
G27 131113 Dimethyl phthalate DMP Plast 0.01 0.01 24 11368 217 1.91
G28 56553 Benz(a)anthracene Benz(a)anthracene PAH 0.01 0.01 0.59 11368 206 1.81
G29 101371 2,4,6-Triallyloxy-1,3,5-triazine TTT Indu 0.01 0.01 62 11368 205 1.80
G30 115968 Tri-(2-chloroethyl) phosphate Tri-(2-chloroethyl) phosphate Indu 0.01 0.01 65 11368 202 1.78
G31 218019 Chrysene Chrysene PAH 0.01 0.01 0.52 11368 188 1.65
G32 122394 Diphenylamine Diphenylamine Pest 0.01 0.01 3 11368 187 1.64
G33 79005 1,1,2-Trichloroethane 1,1,2-trichloroethane HSol 0.01 0.01 14 11368 179 1.57
G34 67129082 Metazachlor Metazachlor Pest 0.01 0.01 44 11368 179 1.57
G35 1241947 2-Ethylhexyl diphenyl phosphate 2-ethylhexyl diphenyl phosphate Indu 0.01 0.01 1 11368 178 1.57
G36 91203 Naphthalene Naphthalene PAH 0.01 0.01 1.5 11368 177 1.56
G37 85018 Phenanthrene Phenanthrene PAH 0.01 0.01 1.2 11368 172 1.51
G38 298464 Carbamazepine Carbamazepine PPCL 0.01 0.01 0.26 11368 170 1.50
G39 86737 Fluorene Fluorene PAH 0.01 0.01 2 11368 161 1.42
G40 128370 Butylated hydroxytoluene BHT PPCL 0.03 0.03 8.7 11368 161 1.42
G41 108907 Chlorobenzene Chlorobenzene HSol 0.01 0.01 1.4 11368 155 1.36
G42 131577 Benzophenone-3 Benzophenone-3 PPCL 0.01 0.01 45 11368 150 1.32
G43 94133 Propylparaben Propylparaben PPCL 0.01 0.01 36 11368 146 1.28
G44 314409 Bromacil Bromacil Pest 0.01 0.01 3.7 11368 139 1.22
G45 83329 Acenaphthene Acenaphthene PAH 0.01 0.01 5 11368 139 1.22
G46 96764 2,4-Di-tert-butylphenol 2,4-DTBP Indu 0.01 0.01 4.6 11368 128 1.13
G47 132649 Dibenzofuran Dibenzofuran Indu 0.01 0.01 0.61 11368 126 1.11
G48 77907 Tributyl acetylcitrate ATBC Plast 0.01 0.01 45 11368 125 1.10
G49 2440224 Drometrizole Drometrizole PPCL 0.01 0.01 18 11368 119 1.05
G50 93049 2-Methyoxynaphthalene Nerolin Indu 0.01 0.01 6 11368 117 1.03

* Key to use codes given in Table 2.2.

Figure 3.2    Box plots of the 50 most frequently detected substances by GC-MS screen. x-axis shown as concentration (mg/L) for all compounds. Due to the high proportion of censored data (censored level shown as red line) summary statistics below this line are not computed.

Discussion of results Pesticides (Pest)[edit]

Eight out of the top 50 most frequently detected compounds using the GC-MS method are pesticides. The triazine herbicides remain prominent. Atrazine is the most frequently detected compound with 1069 detections corresponding to 9.4% of samples, although the concentrations are relatively low, with the 95th percentile (p95) at the LOD and a maximum concentration of 0.75 μg/L. Its TP desethyl-atrazine is also prominent, the 5th most frequently detected compound, with a slightly higher maximum concentration. Simazine is also in the top 50, the 11th most frequently detected compound, but with lower maximum concentrations. Following their withdrawal from use in the UK, in 1993 for amenity use and in 2005 for agricultural uses, concentrations of atrazine and simazine have declined considerably, but concentrations not meeting the drinking water standard still persist in a few places.

The next most frequently detected compound, 2,6-dichlorobenzamide (commonly referred to as BAM) is a TP of the herbicide dichlobenil. The p95 at the LOD, but a number of high concentrations have been measured with a maximum concentration of 70 μg/L.

Metaldehyde is a molluscicide and has been a good example of an emerging contaminant with unanticipated widespread elevated environmental concentrations found over the past decade following development of a suitable analytical method. It has been detected in 2.5% of samples with a maximum concentration of 6.4 μg/L. A ban on the outdoor use of metaldehyde is to be introduced across Great Britain from Spring 2020.

Other pesticides are oxadixyl, a fungicide used in fruit growing, diphenylamine, widely used as an industrial antioxidant and reagent and also employed in agriculture as a fungicide and antihelminthic, and the herbicides metazachlor and bromacil. These are detected in fewer than 2% of samples and have maximum concentrations in the range 3–6 μg/L except metazachlor which has a maximum concentration of 44 μg/L.

These are all compounds with a well-established track record of persistence in groundwater.

Halogenated solvents (Hsol)
Seven out of the top 50 most frequently detected compounds using the GC-MS method are halogenated solvents. Trichloroethene is the most frequently detected compound in this category, and the second overall, with 948 detections corresponding to 8.34% of samples, although the concentrations are relatively low, with a p95 of 0.13 μg/L and a maximum concentration of 184 μg/L. Tetrachloroethene and the THM bromodichloromethane are found with similar maximum concentrations but in fewer samples. Other brominated THMs detected were chlorodibromomethane and bromoform in about 2% of samples. 1,1,2-trichloroethane and chlorobenzene were also found but at lower concentrations. All compounds except trichloroethane and tetrachloroethane had censored distributions with p95 concentrations at the LOD.

Plasticisers (Plast)
Five compounds classified as plasticisers were ranked in the top 50. Of these bisphenol A was the most frequently detected, and was the third most frequent in the dataset, with 939 detections corresponding to 8.26% of samples, with a p95 of 0.09 μg/L and a maximum concentration of 100 μg/L. DEHP was detected in 4% of samples with a maximum concentration of 62 μg/L. N- butylbenzene sulphonamide was much less frequently detected (2.66%) but had a very high maximum concentration (4000 μg/L). Dimethyl phthalate and ATBC were the least frequently detected, but ATBC had a maximum detected concentration of 45 μg/L.

Industrial (Indu)
This is a diverse group of 13 compounds comprising non-chlorinated solvents, industrial intermediates and flame retardants, many of which are also used as plasticisers. All compounds in this group had censored distributions with the p95 concentration at the LOD except cyclohexanone.

Non-halogenated solvents[edit]

Two compounds classed as non-halogenated solvents were detected in the top 50; 1,4-dioxane was detected in 4.6% of samples with a maximum concentration of 63 μg/L and dimethyl adipate in 3.17% of samples but at with a higher maximum concentration of 150 μg/L. As well as a solvent 1,4-dioxane is used as a stabilizer for the transport of halogenated hydrocarbons in aluminum containers. Dimethyl adipate is a nylon precursor and it is also used as a plasticiser as well as a solvent.

Intermediates[edit]

Cyclohexanone is the most frequently detected compound in the Industrial group, found in 5.61% of samples with a maximum concentration of 300 μg/L. This has a wide range of applications and has been used in the manufacture of nylon. Other compounds were found in fewer than 2.5% of samples, TMDD, 1(3H)-isobenzofuranone ((phthalide) can also be used as a food additive), TTT, 2,4-DTBP, dibenzofuran and nerolin. They had maximum concentrations of 6 μg/L or less except TTT, which was found at 62 μg/L.

Flame retardants[edit]

The aryl phosphate esters are mainly used as flame-retardant plasticisers in PVC and other polymers. Triphenyl phosphate is the most widely detected of these, found in 2.91% of samples with a maximum concentration of 2 μg/L. Tri-(2-chloroethyl) phosphate and 2-ethylhexyl diphenyl phosphate were found in 1.78% and 1.57% of samples with maximum concentrations of 65 μg/L and 1 μg/L respectively.

Polyaromatic hydrocarbons (PAHs)
There are 8 compounds in this category. PAHs are generally not very water soluble and are found at low concentrations. Fluoranthene and pyrene are the most soluble of these compounds and are detected in 5.47% and 5.33% of samples respectively with concentrations of 3.4 μg/L and 2 μg/L. Others are detected in fewer than 2% of samples with maximum concentrations of 2 μg/L or less except for acenaphthene which had a maximum concentration of 5 μg/L.

Pharmaceutical, personal care products, lifestyle (PPCL)
Nine of the top 50 compounds were in this category. The p95 of concentration for all of these compounds was below the LOD.

Personal care[edit]

Compounds in this group tend to be applied to the skin. The insect repellent DEET is the most frequently detected compound in the PPCL category and the 7th overall. It was detected in 5.85% of samples with a maximum concentration of 17 μg/L. Benzophenone, benzophenone-3 and drometrizole are UV absorbers and can be used as cosmetics, such as sunscreen, and were found in 2.53% of samples at a maximum concentration of 0.8 μg/L, 1.32% of samples at a maximum concentration of 45 μg/L and 1.05% of samples at a maximum concentration of 18 μg/L respectively. The anti-microbial propyl paraben was detected in 1.28% of samples with a maximum concentration of 36 μg/L.

Pharmaceuticals[edit]

Relatively few pharmaceuticals are detected by the GC-MS method. Carbamazepine was detected in 1.5% of samples with a maximum concentration of 0.26 μg/L.

Food additives[edit]

Butanedioic acid, dimethyl ester was the most frequently detected in this group, and the 4th most frequently overall, being detected in 6.76% of compounds with a maximum concentration of 74 μg/L. It is used as a flavouring agent but also has a wide range of industrial applications. The food antioxidant BHT was detected in 1.43% of samples with a maximum concentration of 8.7 μg/L.

Lifestyle[edit]

Caffeine was detected in 4.26% of samples with a maximum concentration of 1.8 μg/L.

Top 50 GC-MS substances by maximum concentration[edit]

Data description[edit]

The top 50 GC-MS substances ordered by maximum concentration are shown in Figure 3.3. It is worth noting that some of these maximum concentrations (i.e. outliers) are considerably higher than the next highest concentration detected (see Figure 3.2), and they may represent a point source of contamination.

The top 10 highest maximum concentrations in these frequently detected compounds were for benzenesulfonamide, benzotriazole, ethylhexanoic acid, cyclohexanone, cholesterol, mercaplobenzothiazole, benzothiozole, TCE, chlorodibromomethane, and tetrachloroethene.

Figure 3.3    Bar chart of top 50 substances by maximum concentration by GC-MS screen.

Top 50 LC-MS substances by frequency of detection[edit]

Data description[edit]

The top 50 substances from the LC-MS dataset selected by frequency are shown in Figure 3.4. A statistical summary of the data is shown in Table 3.2. Box plots indicating data distribution are shown in Figure 3.5.

The top 18 compounds have sufficient detection data for the statistical distribution to be calculated. Many of these compounds have a median concentration considerably below the LOD. For the majority of these distributions, the p95 is at or close to the LOD. The LOD for the LC-MS method used here are much lower than the GC-MS method and this may well be the main reason why the percentage of detections is much higher.

Figure 3.4    Bar chart of 50 most frequently quantified substances by LC-MS screen.

Figure 3.5 shows the distribution of the results for the 50 most frequently detected substances by LC-MS using a Tukey box plot. The box plots show the interquartile range (IQR), box whiskers (values +/- 1.5 IQR) and outliers (values >1.5 IQR). In many cases the proportion of detections is too low to calculate the IQR and in these instances, the box-plots simply illustrate the outlier concentrations.

Cumulative frequency plots for the 50 most frequently detected substances by LC-MS screens are presented in Figure 3.6.

Table 3.2    Summary statistics for 50 most frequently quantified substances by LC-MS screen. For all analytes the minimum concentration detected was below the LOD. The proportion of positive detections was too low to calculate a 5th percentile value. NA = not statistically valid. Median concentration has been rounded to 6 decimal places. All concentrations are in units of µg/L.
Ranking CAS Number Analyte Short name Use code * LOD Median concentration Mean concentration Standard deviation 95th percentile concentration Maximum concentration Number of analyses Number of positive detections % analyses with positive detections
L1 1007289 Atrazine-desisopropyl (Deisopropylatrazine) Desisopropyl-atrazine Pest 0.001 0.0022 0.0064 0.007 0.02 0.05 267 176 65.92
L2 6190654 Atrazine-desethyl (Desethylatrazine) Desethyl-atrazine Pest 0.001 0.0021 0.018 0.03 0.07 0.3 267 172 64.42
L3 122349 Simazine Simazine Pest 0.001 0.001 0.004 0.005 0.02 0.03 267 170 63.67
L4 1912249 Atrazine Atrazine Pest 0.001 0.001 0.010 0.02 0.04 0.3 267 162 60.67
L5 330541 Diuron Diuron Pest 0.001 0.0005 0.0021 0.008 0.01 0.08 267 133 49.81
L6 298464 Carbamazepine Carbamazepine PPCL 0.001 0.0006 0.0034 0.02 0.02 0.06 267 117 43.82
L7 2971906 Clopidol Clopidol PPCL 0.001 0.0003 0.0045 0.067 0.02 3.5 267 106 39.70
L8 335671 Perfluorooctanoic Acid PFOA Indu 0.005 0.0006 0.0016 0.003 0.006 0.05 267 106 39.70
L9 210880925 Clothianidin Clothianidin Pest 0.001 0.0003 0.003 0.025 0.01 0.09 267 89 33.33
L10 1763231 Perfluorooctane sulfonate PFOS Indu 0.01 0.0002 0.003 0.03 0.01 0.4 267 80 29.96
L11 723466 Sulfamethoxazole Sulfamethoxazole PPCL 0.005 0.0004 0.0016 0.006 0.008 0.03 267 79 29.59
L12 84057841 Lamotrigine Lamotrigine PPCL 0.001 0.0003 0.001 0.003 0.006 0.04 267 76 28.46
L13 25057890 Bentazone Bentazone Pest 0.001 0.0001 0.024 3.8 0.03 0.9 267 75 28.09
L14 150685 Monuron Monuron Pest 0.001 0.0002 0.001 0.005 0.005 0.05 267 67 25.09
L15 34123596 Isoproturon Isoproturon Pest 0.001 0.0002 0.001 0.003 0.005 0.06 267 60 22.47
L16 2706903 Perfluoropentanoic Acid PFPeA Indu 0.005 0.002 0.003 0.003 0.007 0.08 267 60 22.47
L17 307244 Perfluorohexanoic Acid PFHxA Indu 0.005 0.001 0.002 0.003 0.005 0.13 267 60 22.47
L18 17254807 Chloridazon-desphenyl-methyl CDM Pest 0.001 4E-05 0.04 39.3 0.04 1.1 267 56 20.97
L19 56038132 Sucralose Sucralose PPCL 0.01 NA NA NA 0.26 2.3 267 52 19.48
L20 375859 Perfluoroheptanoic Acid PFHpA Indu 0.005 NA NA NA 0.005 0.03 267 50 18.73
L21 133855988 Epoxiconazole Epoxiconazole Pest 0.004 NA NA NA 0.004 0.03 267 47 17.60
L22 188425856 Boscalid (Nicobifen) Boscalid Pest 0.005 NA NA NA 0.008 0.24 267 45 16.85
L23 138261413 Imidacloprid Imidacloprid Pest 0.001 NA NA NA 0.002 0.02 267 43 16.10
L24 60207901 Propiconazole Propiconazole Pest 0.001 NA NA NA 0.006 0.12 267 43 16.10
L25 120068373 Fipronil Fipronil Pest 0.001 NA NA NA 0.001 0.004 267 43 16.10
L26 67129082 Metazachlor Metazachlor Pest 0.001 NA NA NA 0.01 0.8 267 39 14.61
L27 63741 Sulfanilamide Sulfanilamide PPCL 0.01 NA NA NA 0.01 0.037 267 35 13.11
L28 115286 1,4,5,6,7,7-Hexachloro-5- norbornene-2,3-dicarboxylic acid Chlorendic acid Indu 0.005 NA NA NA 0.09 2.1 267 34 12.73
L29 10605217 Carbendazim Carbendazim Pest 0.01 NA NA NA 0.005 0.25 267 33 12.36
L30 23950585 Propyzamide (Pronamide) Propyzamide Pest 0.001 NA NA NA 0.001 0.044 267 32 11.99
L31 76674210 Flutriafol Flutriafol Pest 0.001 NA NA NA 0.01 0.1 267 31 11.61
L32 139402 Propazine Propazine Pest 0.001 NA NA NA 0.001 0.005 267 30 11.24
L33 27203925 Tramadol Tramadol PPCL 0.001 NA NA NA 0.001 0.048 267 29 10.86
L34 1698608 Chloridazon (PAC) Chloridazon Pest 0.001 NA NA NA 0.001 0.03 267 29 10.86
L35 15545489 Chlortoluron (Chlorotoluron) Chlortoluron Pest 0.002 NA NA NA 0.002 0.13 267 27 10.11
L36 142459583 Flufenacet (Fluthiamide) (BAY FOE 5043) Flufenacet Pest 0.001 NA NA NA 0.001 0.057 267 25 9.36
L37 131860338 Azoxystrobin Azoxystrobin Pest 0.001 NA NA NA 0.003 0.02 267 24 8.99
L38 5915413 Terbuthylazine Terbuthylazine Pest NA NA NA 0.001 0.005 267 22 8.24
L39 239110157 Fluopicolide Fluopicolide Pest 0.001 NA NA NA 0.001 0.008 267 21 7.87
L40 7085190 MCPP/Mecoprop MCPP Pest 0.005 NA NA NA 0.01 0.55 267 21 7.87
L41 107534963 Tebuconazole (Terbuconazole) Tebuconazole Pest 0.001 NA NA NA 0.003 0.08 267 21 7.87
L42 153719234 Thiamethoxam Thiamethoxam Pest 0.001 NA NA NA 0.001 0.003 267 20 7.49
L43 137586 Lidocaine (Diocaine) Lidocaine PPCL 0.001 NA NA NA 0.001 0.008 267 20 7.49
L44 120983644 Desthio-prothioconazole Desthio-prothioconazole Pest 0.001 NA NA NA 0.001 0.02 267 20 7.49
L45 2163691 Cycluron Cycluron Pest 0.001 NA NA NA 0.001 0.08 267 19 7.12
L46 87674688 Dimethenamid (SAN 582H) Dimethenamid Pest 0.001 NA NA NA 0.001 0.01 267 18 6.74
L47 422556089 Pyroxsulam Pyroxsulam Pest 0.005 NA NA NA 0.005 0.003 267 18 6.74
L48 64902723 Chlorsulfuron Chlorsulfuron Pest 0.001 NA NA NA 0.001 0.004 267 17 6.37
L49 21087649 Metribuzin Metribuzin Pest 0.002 NA NA NA 0.002 0.03 267 16 5.99
L50 1912261 Trietazine Trietazine Pest 0.005 NA NA NA 0.005 0.18 267 16 5.99

* Key to use codes given in Table 2.2.

Figure 3.5    Box plots for the 50 most frequently detected substances by LC-MS. x-axis shown as concentration (µg/L) for all compounds. Percentiles below the red line, which shows the censored level, were estimated using regression on order statistics (ROS).
Figure 3.6    Cumulative frequency plots for 50 most frequently detected substances by LC-MS, x-axis shown as concentration units of µg/L for all compounds.

Discussion of results[edit]

Pesticides (Pest)
Thirty six of the top 50 compounds most frequently detected are pesticides. The top 4 are all triazine herbicidal compounds: atrazine, the 2 main atrazine TPs and simazine. All 4 are detected in over 50% of samples. Median concentrations ranged from 0.001 to 0.002 μg/L with maximum concentrations in the ranging from 0.03 μg/L for simazine to 0.31 μg/L for atrazine.

Three ‘uron’ herbicides are in the top 15 most frequently detected pesticides: diuron in 49.8% of samples, monuron in 25.1% and isoproturon in 22.5%. Other ‘urons’ detected were chlorotoluron, cycluron and chlorsulfuron.

Other top 50 compounds were the neonicotinoid insecticide clothianidin, the herbicide bentazone and the herbicide TP chloridazon-desphenyl-methyl, all detected in more than 20% of samples. Many of the most frequently detected pesticides are no longer approved for use. The most frequently detected pesticide that is currently approved is bentazone and that was detected in 28% of samples.

Of the other pesticide compounds detected, 2 were insecticides (fipronil and imidacloprid), 9 were fungicides (epoxiconazole, propiconazole, boscalid, carbendazim, azoxystrobin, tebuconazole, fluopicolide, thiamethoxam and the TP prothioconazole-desthio) and the remaining 12 compounds were herbicides (including the parent chloridazon). All were detected in 6% of samples or more. It is interesting that the parent prothioconazole does not appear in the top 50 compounds, although it is detectable by this method. This may relate to the rapid breakdown of the parent molecule in the environment. It was introduced in 2002 as a foliar treatment for fungal diseases in cereals and is still used in the UK.

Compounds with maximum concentrations above the 0.1 μg/L drinking water limit, in descending order of concentration were chloridazon-desphenyl-methyl (1.1 μg/L), bentazone, metazachlor, 2- methyl-4-chlorophenoxyacteic acid (MCPA), atrazine, atrazine-desethyl, carbendazim, boscalid, trietazine, chlorotoluron, propiconazole and flutriafol.

Industrial compounds (Indu)
There are 6 compounds in this group, 5 of which are perfluorinated acids and esters. As might be anticipated, PFOA is the most frequently detected, in 39.7% of samples with a median concentration of 0.0006 μg/L and a maximum concentration of 0.05 μg/L, and PFOS is next, in 30% of samples with a median concentration of 0.0003 μg/L and a maximum concentration of 0.44 μg/L. The other three are the shorter chain acids, PFPeA, PFHxA and PFHpA, present in between 18.7 and 22.4% of samples with maximum concentrations of 0.08, 0.13 and 0.03 μg/L respectively.

Chlorendic acid is an industrial intermediate used in the synthesis of flame retardants and polymers. It is also a common breakdown product of several organochlorine insecticides. It was detected in 12.7% with a maximum concentration of 2.1 μg/L.

Pharmaceutical, personal care products, lifestyle (PPCL)

Pharmaceuticals[edit]

There are eight compounds in this group. The most widely detected compound, and 6th overall is carbamazepine, one of a number of compounds used to treat epilepsy/convulsions/bipolar disorder. This was detected in 43.8% of samples at a median concentration of 0.0006 μg/L and a maximum of 0.61 μg/L. Lamotrigine was also detected in 28.5% with a median concentration of 0.003 μg/L and a maximum of 0.036 μg/L.

Antibiotic and antibacterial compounds were detected: sulfamethoxazole in 29.6% of samples with a median concentration of 0.0004 μg/L and a maximum of 0.03 μg/L, and sulphanilamide in 13.1% with a maximum concentration of 0.037 μg/L.

The analgesics/anaesthetics tramadol and lidocaine were detected in 10.9% and 7.4% of samples respectively at maximum concentrations of 0.048 and 0.008 μg/L respectively.

The veterinary antiprotozoal substance clopidol was detected in 39.7% of samples with a median concentration of 0.0003 μg/L and a maximum concentration of 3.5 μg/L.

Lifestyle[edit]

The artificial sweetener sucralose was detected in 19.5% of samples with a maximum concentration of 2.3 μg/L. Sucralose has been suggested as an indicator of wastewater ingress to groundwater.

Top 50 LC-MS substances by maximum concentration[edit]

Data description[edit]

The top 50 LC-MS substances ordered by maximum concentration are shown in Figure 3.3. It is worth noting that some of these maximum concentrations are considerably higher than the next highest concentration detected (see Figure 3.5), and although they may represent a highly contaminated sample.

The top 10 highest maximum concentrations were for clopidol, followed by sucralose, chlorendic acid, triallate, pentobarbital, chloridazon-desphenyl-methyl, bentazone, tridimefon, metazachlor and mecoprop, with 3 of the top 5 being PPCL compounds.

Figure 3.7    Bar chart of top 50 substances by maximum concentration by LC-MS screen.

Overlap of substances in GC-MS-LC-MS screens[edit]

Comparing the compounds listed in the Top 50 by frequency of detection and Top 50 by concentration for the GC-MS and LC-MS screens identifies 5 compounds which are detected by both methods. These compounds are listed in Table 3.3.

Table 3.3    Compounds quantified by both GC-MS and LC-MS screens, and which were ranked in the Top 50 by frequency of detection and/or concentration.
CAS Number Analyte
122349 Simazine
298464 Carbamazepine
1912249 Atrazine
6190654 Atrazine-desethyl (Desethylatrazine)
67129082 Metazachlor

Analysis of the complete dataset indicates that the GC-MS method detected 663 substances in samples and the LC-MS detected 178 substances. Of these, 81 substances were detected by both methods: these are listed in Table 3.4.

Table 3.4    Compounds quantified by both GC-MS
and LC-MS screens, in the entire BGS database.
CAS Number Analyte
50362 Cocaine
60515 dimethoate
63252 Carbaryl
72446 Methaqualone
76744 Pentobarbital
94757 2,4-D
101428 Fenuron (N,N-Dimethyl-N-phenylurea)
121755 Malathion
122349 Simazine
125406 Butabarbital (Secubarbital)
137586 Lidocaine (Diocaine)
139402 Propazine
150685 Monuron
298464 Carbamazepine
330541 Diuron
330552 Linuron
333415 Diazinon (Dimpylate)
439145 Diazepam
470906 Chlorfenvinphos
486566 Cotinine
551928 Dimetridazole
886500 Terbutryn
1007289 Atrazine-desisopropyl (Deisopropylatrazine)
1014693 Desmetryn
1689845 Bromoxynil
1698608 Chloridazon (PAC)
1912249 Atrazine
1912261 Trietazine
2303175 Triallate
2631405 Isoprocarb
2921882 Chlorpyrifos
5915413 Terbuthylazine
6190654 Atrazine-desethyl (Desethylatrazine)
7287196 Prometryn
15299997 Napropamide
15545489 Chlorotoluron
15687271 Ibuprofen
16118493 Carbetamide
18691979 Methabenzthiazuron
19666309 Oxadiazon
21087649 Metribuzin
21725462 Cyanazine (Fortrol)
23103982 Pirimicarb
23950585 Propyzamide (Pronamide)
25057890 Bentazone
26225796 Ethofumesate
28721075 Oxcarazepine
29232937 Pirimiphos-methyl (Pirimifos-methyl)
34123596 Isoproturon
40487421 Pendimethalin (Penoxalin)
43121433 Triadimefon
51235042 Hexazinone
53112280 Pyrimethanil
55219653 Triadimenol
55335063 Trichlopyr
57837191 Metalaxyl
60142963 Gabapentin
60168889 Fenarimol
60207901 Propiconazole
66246886 Penconazole
66332965 Flutolanil
67129082 Metazachlor
67564914 Fenpropimorph (Ro 14-3169)
67747095 Prochloraz
76674210 Flutriafol
77732093 Oxadixyl
85509199 Flusilazole
87674688 Dimethenamid (SAN 582H)
107534963 Tebuconazole (Terbuconazole)
110488705 Dimethomorph
120068373 Fipronil
121552612 Cyprodinil
123312890 Pymetrozin
131860338 Azoxystrobin
133855988 Epoxiconazole
142459583 Flufenacet (Fluthiamide) (BAY FOE 5043)
153719234 Thiamethoxam
183675823 Penthiopyrad
188425856 Boscalid (Nicobifen)
239110157 Fluopicolide
361377299 Fluoxastrobin

Spatial plots of occurrence of selected substances[edit]

This section presents a series of spatial plots of key substances. These were selected on the basis of frequency of detection and/or being classed as PPCL, a large group of substances of potential emerging concern which is receiving growing attention in Europe. Concentrations (maximum per site) are shown as proportional symbols. Results are plotted on a background of a simplified 1:625 000 scale geological map as requested by the EA: the legend is provided in Figure 3.8.

Figure 3.8    Geological map background (1:625 scale bedrock geology — UK onshore bedrock age) with legend.

GC-MS[edit]

Atrazine remains the most frequently detected compound by GC-MS. Since the database contains data collected throughout the period that this method has been used, it may give a misleading impression of current conditions. A spatial plot of these data (Figure 3.9) shows that atrazine is predominantly detected at concentrations of >0.1 µg/L in the principal aquifers of the Chalk and the Permo-Triassic sandstone. This may reflect historical usage and particularly for the Chalk the travel time from the surface through the unsaturated zone to the water table and the slow rate of flushing of these aquifers.

Historically atrazine was used for weed control, both in agriculture and for amenity use until 1992 when it was withdrawn from non-agricultural uses in the UK. There was concern that amenity use potentially allowed pesticide to enter the subsurface via soakaways, bypassing the soil. Limited agricultural uses were permitted until an EU-wide ban for all uses followed in 2003. The elevated concentrations seen in this dataset demonstrate that a precautionary approach is needed to protect groundwater from pesticides as degradation rates in the subsurface are typically very slow.

  • Figure 3.9    Spatial plot of atrazine concentrations by
    GC-MS screen (µg/L).
  • Figure 3.10    Spatial plot of BPA concentrations by GC-MS screen (µg/L).

BPA is the most frequently detected plasticiser in the dataset. The spatial plot (Figure 3.10) shows it to be widely detected across England. There are areas of concentrations >1 µg/L in the urban areas of Greater London and the Thames Estuary, Birmingham, Liverpool and Hull areas and in the Jurassic limestones of Lincolnshire and perhaps surprisingly in the far southwest.

There are likely to be multiple sources of BPA in the environment, including wastewater, septic tanks and landfills. It is also a common component of many plastic items and care is needed to exclude these from sampling equipment. Plasticisers can be leached into groundwater from plastic well casing and pipework associated with groundwater sampling and this could explain BPA detections at some sites rather than BPA occurrence in the aquifer.

DEET is the second most frequently detected PPCL in the dataset. Figure 3.11 shows higher concentrations to be distributed with areas of central southern England, the north Yorkshire coast and the Manchester-Liverpool area with groups of values over 0.1 µg/L. The Lincolnshire Limestone and the south east of England also show scattered higher concentrations.

When used as an insect repellent, DEET is topically applied and may therefore be found in the wastewater stream (Aronson et al., 2012[1]). DEET can be readily absorbed into the body of plastic objects. The spatial coherence of DEET observations in some regions suggests that some detections may be due to contamination from samplers, but this has not been verified.

Butanedioic acid, dimethyl ester (dimethyl succinate) is detected widely across England, with surprisingly few detections in the Chalk of south-east England, the Carboniferous and Devon and Cornwall (Figure 3.12).

Caffeine is also widely detected in groundwater across England with pronounced clusters of detections in the London area, Cornwall and North Yorkshire (Figure 3.13).

  • Figure 3.11    Spatial plot of DEET concentrations by GC-MS screen (μg/L).
  • Figure 3.12    Spatial plot of butanedioic acid, dimethyl ester (dimethyl succinate) concentrations by GC-MS screen (μg/L).
  • Figure 3.13    Spatial plot of caffeine concentrations by GC-MS screen (μg/L).

LC-MS[edit]

There are considerably fewer LC-MS data and these are confined to selected regions of the EA. Carbamazepine is the most frequently detected PPCL in the LC-MS database. The spatial plot (Figure 3.14) shows sampling to be mainly restricted to the central and southern areas of England, with some sampling in the northeast. Carbamazepine is detected in the London area, in the Chalk of the southeast and in the Permo-Triassic sandstone. There is insufficient data to comment on controls on spatial distribution.

Figure 3.14    Spatial plot of carbamazepine concentrations by LC-MS screen (μg/L).

Detections of clothianidin were found in Gloucestershire and Oxfordshire, in London and in Sussex/Hampshire (Figure 3.15). Presumably, this is associated with the distribution of the target insect pests, but there are too few datapoints to allow comment on spatial distribution.

PFOS and PFOA were mainly detected in the London area, some of which are possibly associated with the Buncefield fire in 2005 and the extensive use of foams to supress the fire (Figure 3.16 and Figure 3.17). Other localised detections include in Hampshire, two sites near the coast in north east England, and a site in Birmingham. PFOS and PFOA are also degradation products of other precursor substances not reported in the LC-MS target screening method.

Clopidol was detected in µg/L concentrations at only a small number of sites, possibly associated with livestock farming and the veterinary use of this substance to treat Coccidia parasites. A high proportion of detections at low concentrations give rise to its prominence in Figure 3.18, but initial results do not indicate a wide distribution in groundwater at µg/L concentrations, however the spatial sampling is limited.

  • Figure 3.15    Spatial plot of clothianidin concentrations by
    LC-MS screen (μg/L).
  • Figure 3.16    Spatial plot of PFOS concentrations by
    LC-MS screen (μg/L).
  • Figure 3.17    Spatial plot of PFOA concentrations by
    LC-MS screen (μg/L).
  • Figure 3.18    Spatial plot of clopidol concentrations by
    LC-MS screen (μg/L).

References[edit]

  1. ARONSON, D, WEEKS, J, MEYLAN, B, and HOWARD, P. 2012. Environmental release, environmental concentrations, and ecological risk of N,N-Diethyl-m-toluamide (DEET). Integrated Environmental Assessment and Management, 8, 1, 135–166.