Bioindicators add valuable understanding of biological impacts to contaminant monitoring programs. However, attributing effects (e.g., mortality and growth impairment) to contaminant exposures is challenging because of potential confounding by environmental variables. We assessed the influence of four water quality variables (temperature, dissolved oxygen, pH, and conductivity) on contaminant effects assessments during in situ exposures of the amphipod Hyalella azteca in six agricultural and urban watersheds in southern Ontario, Canada (2005–06, 2008–10). We further tested whether sampling in specific months of the growing season would minimize confounding effects. While high toxicity from organophosphate and carbamate pesticides increased mortality and reduced growth in caged amphipods, warmer stream temperatures also affected endpoints, increasing mortality and improving growth. Seasonal patterns indicated early summer (June) as optimal for detecting impacts when: (1) stream pesticide concentrations were highest, (2) acetylcholinesterase (AChE) inhibition (a biomarker of organophosphate/carbamate exposure) was highest, and (3) stream temperature was below its seasonal peak. Specifically, higher correlations among organophosphate pesticide concentrations, AChE inhibition, and mortality indicated better attribution of cause in this month (r = 0.53—0.76, p < 0.05). Ability to discriminate between pesticide-impacted sites and reference sites was also greater than other months (June = 100

Triclosan is widely used in personal care products (skin creams, toothpastes, soaps, deodorants, body spray) and cleaning products (dishwashing detergent and all-purpose cleaners) (Halden in Environ Sci Technol 48:3603–3611, 2014). In 2001, it was selected for screening-level risk assessment under the Canadian Environmental Protection Act (HC and EC in Preliminary assessment. Triclosan. Chemical abstracts Service Number 3380-34-5, 2012. http://www.ec.gc.ca/ese-ees/default.asp?lang=En&n=6EF68BEC-1), and its physicochemical and toxicological characteristics indicate that there may be a risk to aquatic environments due to releases of the chemical in Canada. A surveillance initiative across Canada has included sampling at 44 sites from July 2012 to March 2018. Triclosan was detected in 226 of 918 samples; concentrations ranged from less than 6 to 874 ng L−1, and the detections averaged 54.23 ng L−1 (standard deviation; 97.6 ng L−1). However, using the entire dataset (including censored data estimated with the Kaplan–Meier model), the mean triclosan concentration was 17.95 ng L−1, and the standard deviation was 52.84 ng L−1. Three samples at Wascana Creek (downstream), Saskatchewan, had concentrations above the Federal Environmental Quality Guidelines of 470 ng L−1, indicating a potential risk to the aquatic ecosystem. In this study, triclosan in samples collected downstream from municipal wastewater treatment plant discharges usually demonstrated higher concentrations than upstream samples. Based on the results of this study, it is hypothesized that triclosan concentration have fluctuated between years of this study but not in an overall or significant increase or decreasing trend. Triclosan concentrations and detections also are more prevalent in urban than in rural or mixed development rivers. Performance evaluation of triclosan concentrations in the Canadian environment is scheduled to be reassessed by 2024. Therefore, a 3-year sampling program should be in place across Canada by 2021.

The widespread use of neonicotinoid insecticides and recent increased regulatory scrutiny requires the generation of monitoring data with sufficient scope and resolution to provide decision makers with a better understanding of occurrence and distribution in the environment. This study presents a wide scale investigation of neonicotinoid insecticides used across the range of agricultural activities from fifteen surface water sites in southern Ontario. Using statistical analysis, the correlation of individual compounds with land use was investigated, and the relationship between neonicotinoid occurrence and hydrologic parameters in calibrated water courses was also assessed. Of the five neonicotinoids studied, imidacloprid, clothianidin and thiamethoxam exhibited detection rates above 90% at over half the sites sampled over a three year period (2012-2014). At two sites in southwestern Ontario, the Canadian Federal freshwater guideline value for imidacloprid (230 ng/L) was exceeded in roughly 75% of the samples collected. For some watersheds, there were correlations between the occurrence of neonicotinoids and precipitation and/or stream discharge. Some watersheds exhibited seasonal maxima in concentrations of neonicotinoids in spring and fall, particularly for those areas where row crop agriculture is predominant; these seasonal patterns were absent in some areas characterized by a broad range of agricultural activities. Crown Copyright (C) 2016 Published by Elsevier Ltd.

Surface water sampling in 2007-2010 measured the occurrence of carbamates and metalaxyl during base flow conditions and wet weather events in southern Ontario surface waters. Carbaryl, metalaxyl and pirimicarb were the most frequently detected compounds. In 2008 these three compounds were detected in over 50 % of the samples. Overall mean concentrations of carbaryl and metalaxyl over the course of the study (2007-2010) were 15 and 18 ng/L, respectively. Elevated concentrations of carbaryl (~100 to ~950 ng/L) appeared associated with wet weather (high flow) events, while highest concentrations of metalaxyl (~20-1330 ng/L) were correlated with base flow conditions. We attributed these observations as the result of runoff of carbaryl from the watershed during rain events, while metalaxyl contamination may have resulted primarily from spray drift.

BACKGROUND The objective of this study was to investigate the occurrence of glyphosate residues (glyphosate and its metabolite AMPA) in shallow groundwater in a catchment dominated by agriculture, and to examine the potential for this groundwater to store and transmit these compounds to surface waters. RESULTS Glyphosate residues were found in some of the groundwater samples collected in riparian (surface seeps), upland (mostly <20 m below ground) and wetland settings (<3 m below ground). Overall, glyphosate and AMPA were detected in 10.5 and 5.0%, respectively, of the groundwater samples analyzed as part of this study. All concentrations of glyphosate were well below Canadian guidelines for drinking water quality and for protection of aquatic life. Seasonal differences in concentrations in riparian seeps were possibly related to cycles of weather, herbicide application and degradation of glyphosate. Highest concentrations were at upland sites (663 ng L(-1) of glyphosate, 698 ng L(-1) of AMPA), apparently related to localized applications. Most glyphosate detections in wetlands were >0.5 km distant from possible areas of application, and, combined with other factors, suggest an atmospheric transport and deposition delivery mechanism. In both upland and wetland settings, highest glyphosate concentrations were sometimes not at the shallowest depths, indicating influence of hydrological factors. CONCLUSION The glyphosate/AMPA detections in riparian seeps demonstrated that these compounds are persistent enough to allow groundwater to store and transmit glyphosate residues to surface waters. Detections in the wetlands support earlier evidence that atmospheric transport and deposition may lead to glyphosate contamination of environments not intended as targets of applications. This interpretation is further supported by detections of both glyphosate and AMPA in precipitation samples collected in the same watershed. © 2016 Her Majesty the Queen in Right of Canada Pest Management Science © 2016 Society of Chemical Industry.

In situ exposures with Hyalella azteca were used to assess impacts of current‐use pesticides in Southern Ontario, Canada. Exposures were conducted over 2 growing seasons within areas of high pesticide use: 1 site on Prudhomme Creek and 3 sites on Twenty Mile Creek. Three sites on Spencer Creek, an area of low pesticide use, were added in the second season. Surface water samples were collected every 2 wk to 3 wk and analyzed for a suite of pesticides. Hyalella were exposed in situ for 1 wk every 4 wk to 6 wk, and survival and acetylcholinesterase (AChE) activity were measured. Pesticides in surface waters reflected seasonal use patterns: lower concentrations in spring and fall and higher concentrations during summer months. Organophosphate insecticides (chlorpyrifos, azinphos methyl, diazinon) and acid herbicides (2,4‐dichlorophenoxyacetic acid [2,4‐D], mecoprop) were routinely detected in Prudhomme Creek, whereas neutral herbicides (atrazine, metolachlor) dominated the pesticide signature of Twenty Mile Creek. Spencer Creek contained fewer pesticides, which were measured at lower concentrations. In situ effects also followed seasonal patterns: higher survival and AChE activity in spring and fall, and lower survival and AChE activity during summer months. The highest toxicity was observed at Prudhomme Creek and was primarily associated with organophosphates. The present study demonstrated that current‐use pesticides in Southern Ontario were linked to in situ effects and identified sites of concern requiring further investigation. Environ Toxicol Chem 2016;35:1224–1238. © 2015 Crown in the Right of Canada.

Surface water concentrations of the acid herbicides 2,4-D, dicamba and mecoprop were measured in ten urban Ontario streams before (2003–2008) and after (2009–2012) a ban on the sale and use of pesticides for cosmetic (non-essential) purposes. Frequencies of detection (2003–2012) were 98%, 96% and nearly 100%, respectively for 2,4-D, dicamba and mecoprop. Concentrations were typically in the ng L−1 range, although periodic spikes in the µg L−1 range were observed. Concentrations in a majority of the study streams decreased significantly following the cosmetic pesticides ban. Concentrations decreased from 16% to 92% depending on the stream and herbicide. The presence of these herbicides in urban streams was likely a result of urban applications. Concentrations were significantly related to population density or urban land cover, and the relative proportion of the three herbicides observed in urban stream water approximated the ratios found in pesticide products formulated for urban use. Longer-term trends indicate that decreases in stream water herbicide concentrations may have preceded the ban and may be related to increased public awareness of pesticide issues and voluntary reductions in urban pesticide use.

In Canada, perfluoroalkyl acids (PFAAs) have been the focus of several monitoring programs and research and surveillance studies. Here, we integrate recent data and perform a multi-media assessment to examine the current status and ongoing trends of PFAAs in Canada. Concentrations of perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and other long-chain perfluorocarboxylates (PFCAs) in air, water, sediment, fish, and birds across Canada are generally related to urbanization, with elevated concentrations observed around cities, especially in southern Ontario. PFOS levels in water, fish tissue, and bird eggs were below their respective Draft Federal Environmental Quality Guidelines, suggesting there is low potential for adverse effects to the environment/organisms examined. However, PFOS in fish and bird eggs tended to exceed guidelines for the protection of mammalian and avian consumers, suggesting a potential risk to their wildlife predators, although wildlife population health assessments are needed to determine whether negative impacts are actually occurring. Long-term temporal trends of PFOS in suspended sediment, sediment cores, Lake Trout (Salvelinus namaycush), and Herring Gull (Larus argentatus) eggs collected from Lake Ontario increased consistently from the start of data collection until the 1990s. However, after this time, the trends varied by media, with concentrations stabilizing in Lake Trout and Herring Gull eggs, and decreasing and increasing in suspended sediment and the sediment cores, respectively. For PFCAs, concentrations in suspended sediment, sediment cores, and Herring Gulls generally increased from the start of data collection until present and concentrations in Lake Trout increased until the late 1990s and subsequently stabilized. A multimedia comparison of PFAA profiles provided evidence that unexpected patterns in biota of some of the lakes were due to unique source patterns rather than internal lake processes. High concentrations of PFAAs in the leachate and air of landfill sites, in the wastewater influent/effluent, biosolids, and air at wastewater treatment plants, and in indoor air and dust highlight the waste sector and current-use products (used primarily indoors) as ongoing sources of PFAAs to the Canadian environment. The results of this study demonstrate the utility of integrating data from different media. Simultaneous evaluation of spatial and temporal trends in multiple media allows inferences that would be impossible with data on only one medium. As such, more co-ordination among monitoring sites for different media is suggested for future sampling, especially at the northern sites. We emphasize the importance of continued monitoring of multiple-media for determining future responses of environmental PFAA concentrations to voluntary and regulatory actions.

Water quality monitoring programs rely on residue data that are frequently left censored, due to some observations occurring below the Method Detection Limit (MDL). Our objective was to determine the influence the MDL has on the interpretation of pesticide residues in surface waters. Water samples from tributaries in southern and central Ontario were collected by Environment Canada from 2003 to 2008 and were analyzed for 27 pesticides, with MDLs that averaged 7.02 ng(-1) L (range 0.39-25.1 ng(-1) L). We then simulated MDLs ranging from 25 to 1700 ng(-1) L, to determine the impact this would have on the reporting of pesticide concentrations and detections. The mean number of pesticides detected simultaneously declined with increasing, i.e. less sensitive MDLs, from 5.02 pesticides (native MDL) to 0.08 pesticides detected (MDL<1700 ng(-1) L). We compared the proportion of sites where pesticides were detected in surface waters under five MDL scenarios for 13 selected pesticides. The proportions decreased sharply with increasing MDLs. We calculated detection probabilities in an effort to compensate for higher MDLs using maximum likelihood; while adjusting for detection probabilities generally improved estimates of the presence of pesticides, as the MDLs increased the ability to compensate for detection probabilities deteriorated and became unviable at high MDLs. Depending on the method of substitution for observations below MDL (replacement with ½ × or 0 × MDL), the mean and median pesticide residues became increasingly over- and underestimated, respectively, at higher MDLs. Although monitoring programs that are focused on exceedences of water quality guidelines may not require low MDLs, the achievable goals of monitoring programs oriented towards other ecological and toxicological objectives may be limited by higher MDLs.

Surface water sampling in 2006–2008 measured the occurrence of sulfonylureas and related herbicides (SUs) during base flow conditions and wet weather events. Flumetsulam (29.2%), diuron (36.5%) and fomesafen (25.3%) were most frequently detected over the course of the study. Typical SU concentrations were in the low parts per trillion range; however, maximum concentrations of fomesafen (873 ng/L), linuron (856 ng/L) and diuron (2,900 ng/L) approached or exceeded 1 μg/L. The temporal trend in SUs showed a correlation with application periods. In general, detections of SUs were more frequent where rotation of row crops was more intense. Sampling during wet-weather events indicated potential for a range of SUs to be flushed into surface waters at relatively high concentrations.

During the past decade, the invasive Phragmites australis (common reed) has established itself along beaches of the Great Lakes. causing detrimental impacts to both the natural ecological integrity of the shoreline and the recreational value of beaches. The herbicide Roundup (R), containing the active ingredient glyphosate, was applied to Phragmites along a beach on the southern shore of Georgian Bay, Canada, to eradicate the Phragmites which was destroying the natural beach ecosystem. Groundwater and lake water were tested to determine if glyphosate enters the groundwater and lake at the beach and how long glyphosate will persist. Two days after application, the geometric mean concentration of glyphosate in the groundwater below the Phragmites was 0.060 mu g/L with a maximum of 12.50 mu g/L Concentrations rapidly declined over the next two to three weeks to below minimum detection limits (<0.020 mu g/L). Glyphosate was also detected in the nearshore lake water with concentrations peaking at a geometric mean of 0.14 mu g/L one week after application, and declining to 0.039 mu/L four weeks after application. Concentrations of glyphosate never exceeded the Canadian water quality guideline for the protection of aquatic life (65 mu g/L) in either the groundwater or lake water. An approximate half-life for the dissipation of glyphosate by degradation and dilution/flushing as groundwater flows toward the lake, assuming a first order kinetic reaction, yielded a half-life of 3.5 during the 4 weeks after the herbicide was applied. The application of Roundup (R) resulted in an 90% reduction in the size of the stand of Phragmites. Crown Copyright (C) 2011 Published by Elsevier B.V. on behalf of International Association for Great lakes Research. All rights reserved.

A model formulation based on “aquivalence”, as defined in terms of activity is presented to estimate the multimedia fate of ionizing chemicals. The aquivalence approach is analogous to fugacity but aquivalence is applicable to neutral and ionizing compounds, and has been applied previously to speciating chemicals, notably metals. The new aquivalence-based mass-balance model treats ionizing organic compounds that exist as interconverting neutral and ionic species which are subject to fate processes at differing rates. The model is illustrated by application to four ionizing pharmaceuticals in Hamilton Harbour, Lake Ontario. At the system pH of 7.9–8.5, ibuprofen, gemfibrozil, and naproxen are expected to be almost entirely ionic and triclosan split between ionic and neutral forms. Measured seasonal surface water concentrations, which were 2–10 times lower in the late summer and fall than during spring, were used to solve for unknown values of chemical half-life in the water column due to degradation (photo- and bio-) of the ionizing and neutral forms and secondarily, ionic sorption coefficients of the ionizing forms. Model estimates of half-lives in the habour's water ranged from 11 to 77, 11 to 147 and 10 to 37 for ionic ibuprofen, gemfibrozil, and naproxen, respectively; and 4–22days and 2–9days for ionic and neutral triclosan, respectively, with the shortest half-lives in spring and the longest in summer.

The Great Lakes have been the focus of intensive long-term research and monitoring programmes for the past 40 years. Spatial distributions and temporal trends have been determined for a range of environmental compartments, including surface water, sediment and fish. In general, there have been dramatic reductions in contamination by legacy pollutants including polychlorinated biphenyls (PCBs), organochlorine pesticides and metals. Concentrations of PCBs and lead in surface water at the mouth of the Niagara River have decreased by 58 and 54%, respectively, over the period 1986–2007. Correspondingly, concentrations of PCBs and lead in offshore sediments of Lake Ontario have decreased by 37 and 45%, respectively, since peak accumulations in the 1970s. Temporal trends for more modern chemicals, including polybrominated diphenylethers and perfluoroalkyl compounds, showed increases up until 2000 when management actions and heightened stakeholder awareness resulted in a levelling off or decline in the subsequent time period. While legacy issues are largely associated with areas of historical industrial activity, the presence of newer chemicals is generally associated with modern urban/industrial areas that act as diffuse sources.

INTRODUCTION:Public and scientific concern has grown over the last decade in Canada over the cosmetic use of pesticides in urban centers. With this in mind, a national survey was designed to monitor eight commonly used herbicides in urban rivers and streams across Canada.MATERIALS AND METHODS:To coordinate sample collections across the country, samples were collected monthly on one of two predetermined dates from April to September, 2007 from 19 sites within 16 watersheds, including 15 sites downstream of urban lands and two reference sites. Water samples were also collected approximately three times from each watershed during or after precipitation events. All samples were collected using a common sampling protocol and all were analyzed using the same analytical laboratories.RESULTS AND DISCUSSION:The herbicides 2,4-D, mecoprop, dicamba, glyphosate and its major metabolite aminomethylphosphonic acid (AMPA) were most frequently detected. Using either herbicide concentrations upstream/downstream of urban centers or bromoxynil and clopyralid as indictors of agricultural inputs of herbicides to streams, it was clear that environmental concentrations of these herbicides downstream of urban areas were linked to urban use in Canada. Herbicide concentrations in streams draining urban areas were greater during or after significant rainfall events and, with the exception of glyphosate, were significantly greater in the Province of Ontario. Herbicide concentrations were not correlated to the proportion of the watersheds in urban land use. Also, there was no difference in seasonal patterns of herbicide concentrations across urban centers when grouped in five geographic areas. None of the herbicide concentrations measured exceeded existing Canadian Water Quality Guidelines for the protection of aquatic life.CONCLUSIONS:This is the first time a national survey of pesticides in urban rivers has been carried out in a consistent fashion across Canada. Concentrations of 2,4-D, mecoprop, dicamba, glyphosate, and AMPA were linked to urban use and frequently detected in all geographic areas. However, geographic differences in concentration suggested differences in usage or stream connectivity patterns among urban centers. Some jurisdictions in Canada have recently restricted cosmetic use of pesticides and it would be interesting to determine whether such restrictions will lead to reduced pesticide concentrations in urban streams.

Concerns regarding the impacts of pesticides on aquatic species and drinking water sources have increased demands on water quality monitoring programs; however the costs of sample analysis can be prohibitive. In this study we investigated enzyme-linked immunosorbent assay (ELISA) as a cost-effective, high through-put method for measuring pesticide concentrations in surface waters. Seven hundred and thirty-nine samples from 158 locations throughout Ontario were analysed for atrazine and metolachlor from April to October 2007. Concentrations ranged from <0.1 to 3.91 μg L−1 (median = 0.12 μg L−1) for atrazine and from <0.1 to 1.83 μg L−1 (median = 0.09 μg L−1) for metolachlor. Peak concentrations occurred in late spring/early summer, in rural agricultural locations, and decreased over the remainder of the growing season for both herbicides. About 3% of the samples that had ELISA results occurring above the limit of quantification (0.10 μg L−1) were evaluated against gas chromatography-mass spectrometry (GC–MS). Linear regression analysis revealed a R2 value of 0.88 and 0.39, for atrazine and metolachlor, respectively. ELISA tended to overestimate concentrations for atrazine and metolachlor, most likely because the ELISA kits also detect their metabolites. Atrazine data suggest that ELISA may be used complementary with GC–MS analysis to enhance the spatial and temporal resolution of a water quality monitoring study. The commercially available metolachlor ELISA kit requires further investigation. ELISA may be used to detect atrazine and metolachlor in surface water samples, but it is not recommended as a quantitative replacement for traditional analytical methods.

Mecoprop, dichlorprop and metolachlor concentrations and enantiomer signatures were determined in Ontario streams in 2006-2007 and compared to results from 2003 to 2004. Median concentrations of dichlorprop and metolachlor were not significantly different between the two campaigns, but mecoprop was higher in 2006-2007. Concentrations of mecoprop and dichlorprop in Lake Ontario surface water were 1-2 orders of magnitude lower than stream averages. Enantiomer fractions (EFs) > 0.5 of mecoprop in high-concentration stream water samples during 2006-2007 were related to replacement of racemic mecoprop by single (+) enantiomer mecoprop-P after 2004. EFs <0.5 in low-concentration samples suggested enantioselective degradation and/or interconversion. Metolachlor profiles were expressed as SF, the fraction of herbicidally active/(active + inactive) stereoisomers. Samples with higher concentrations of metolachlor had SFs similar to S-metolachlor which is enriched in the active stereoisomers. Low concentrations were associated with lower and more variable SFs, suggesting mixed input of racemic and S-metolachlor or stereoselective degradation. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

Intensive row crop agriculture (IRCA) for corn and soybean production is predominant in eastern and central North America. IRCA relies heavily on pesticide and nutrient inputs to maximize production under conventional systems. In 2003-2005, we assessed the occurrence of a suite of potential endocrine effects in amphibians inhabiting farm ponds and agricultural drains in IRCA areas of southwestern Ontario. Effects were compared to amphibians from two agricultural reference sites as well as four non-agricultural reference sites. Pesticide and nutrient concentrations were also determined in water samples from those sites. Atrazine and metolachlor were detected in most samples, exceeding 1 microg L(-1) at some sites. Blood samples were taken from northern leopard frogs (Rana pipiens) and green frogs (Rana clamitans) for analysis of circulating sex steroids and vitellogenin-like protein (Vtg-lp), a biomarker of exposure to environmental estrogens. Gonads were histologically examined for evidence of abnormalities. Some evidence of exposure to endocrine disrupting compounds was apparent from the data. The occurrence of testicular ovarian follicles (TOFS) in male R. pipiens was significantly higher (42%; p<0.05) at agricultural sites, particularly those in Chatham county compared to frogs from reference sites (7%). There was no difference in circulating sex steroid levels between frogs from agricultural and reference sites and sex steroid levels did not correlate with pesticide concentrations in the environment. No differences were detected in the gonadosomatic indices or stage of spermatogenesis between frogs from agricultural and non-agricultural regions (p>0.05). Plasma Vtg-lp was detected in only one male R. pipiens from an agricultural site. Neither gonad size, gonad maturity nor sex steroid levels differed between normal males and those with testicular oocytes. Although the proportion of testicular oocytes did not correlate directly with atrazine concentrations, it did correlate with a mixture of pesticides and nutrients, particularly atrazine and nitrate, while the number of pesticides detected at each site was also important.

Concentrations of mecoprop, dichlorprop, and metolachlor were investigated in 393 samples from Ontario streams in 2003-2004. Maximum concentrations of mecoprop, dichlorprop, and metolachlor were 1900, 6.62, and 1560 ng L(-1), respectively in 2003, and 103,000, 110, and 5290 ng L(-1), respectively, in 2004. Concentrations of metolachlor in agricultural watersheds were significantly (p < 0.0001) higher than those in urban watersheds, whereas concentrations of mecoprop did not differ (p > 0.1) between the two watershed types. Enantiomer fractions (EFs) of the acid herbicide mecoprop ranged from 0.236 to 0.928 and for dichlorprop EFs ranged from 0.152 to 0.549. EFs of mecoprop did not differ significantly (p > 0.1) between agricultural and urban land usage. Mecoprop EFs > or = 0.5 were found in 54% of samples, a situation expected during the transition years when racemic mecoprop was replaced by mecoprop-P, consisting of only the R(+) enantiomer. However, EFs < 0.5 were found in 46% of samples, which suggests preferential degradation of R(+) or conversion of R(+) to S(-). The four stereopluisomers of metolachlor were separated by HPLC and are reported as the ratio of the two herbicidally active stereoisomers (aS,1'S and aR,1'S) to the two inactive stereoisomers (aS,1'R and aR,1'R). The average S/R of metolachlor in streams was 6.73 +/- 2.28 and ranged from 1.08 to 12.7. Samples with higher concentrations of metolachlor had S/R ratios similar to the S/R of S-metolachlor (enriched in aS,1'S and aR,1'S stereoisomers) whereas samples with lower concentrations display lower S/R ratios with greater variability, suggesting mixed input of racemic and S-metolachlor or stereoselective degradation. S/R values were significantly higher (p < 0.001) in agricultural than urban watersheds. Streamwater from row crop areas showed higher S/R ratios than streamwater from fruit growing areas (p = 0.036).

Glyphosate in surface waters of southern Ontario (Canada) was studied over a 2-year period. A small percentage of samples exhibited glyphosate concentrations greater than the analytical limit of quantitation (17 μg a.e./L), and the maximum concentration of glyphosate measured was 40.8 μg/L. No samples of roughly 500 analyzed exceeded the Canadian Water Quality Guideline of 65 μg a.e./L considered protective of aquatic life. Typical concentrations of glyphosate in amphibian habitats were well below a range of toxicity thresholds for aquatic organisms, and were thus judged to be unlikely to pose a substantial risk to either sensitive amphibian larvae or other aquatic biota.