Pesticide Toxicity Index Research Articles

Use of the Pesticide Toxicity Index to Determine Potential Ecological Risk in the Santiago-Guadalajara River Basin, Mexico

The Santiago-Guadalajara River Basin (SGRB), located in western Mexico, is one of the most polluted rivers in the country. A pesticide monitoring program was carried out from January 2022 to September 2022, during which time water samples collected at 25 sites in the main stem and tributaries revealed the presence of 13 of the 24 pesticides analyzed, including α-BHC, β-BHC, γ-BHC (Lindane), γ-Chlordane, Hexachlorobenzene, Heptachlor, Aldrin, α-Endosulfan, DDT, -4,4, Methoxychlor, Chlorpyrifos-methyl, Endosulfan sulfate, and Dicofol. A high level of correlation was found between the identified pesticides, which could mean that several of these pesticides reached a stable level within the monitored water bodies. Most of the identified pesticides are classified as high environmental risk according to the Stockholm Convention because of their persistence and high degree of toxicity to the environment and human health. A Pesticide Toxicity Index (PTI) was applied to identify the streams considered to be of concern due to the presence of pesticides exceeding the threshold limits established by national and international guidelines. Performing a calculation for the entire Santiago-Guadalajara River Basin, the PTI reached a value of 0.833, which, according to the criteria of this method, classifies it as a “Moderate” level of risk for aquatic life. Increased regulatory and surveillance measures by state and federal authorities are required to prevent the use of these pesticides, which have been restricted globally.

Monitoring and accumulative risk assessment of pesticide residues detected in the common vegetables grown in the Eastern Nile Delta, Egypt

The present study proposed to monitor the pesticide residues in most vegetables grown in the Eastern Nile Delta region, Egypt, and evaluate the potential health risk associated with them. Using multi-analysis methods, twenty-five pesticide residues were found. Pesticide residues were found in 88.37% of examined samples, with 31.4% above maximum residue limits. Overall, 66.23% of contaminated samples contain more than one pesticide, while three samples (1.2%) contain residues of 6 compounds. Residues of 25 chemicals were found in tested samples, with chlorpyrifos being the most common at 25.6%. According to the WHO toxicity classification (WHO, 2019), 36% of detected compounds were moderately hazardous (class II) and 24% slightly hazardous (class III). The health index values were less than 100%, indicating that there was an acceptable safety risk for exposure to the individual pesticide. However, the combined risk index revealed an unacceptable risk to individuals more than the individual health index because the pesticide toxicity index values were greater than 1.0 in some vegetables. There is a critical need to monitor and control the pesticide residues in vegetables to standardize the pesticide amount used and reduce their misuse.

Concentration levels and risk assessment of organochlorine and organophosphate pesticide residue in selected cereals and legumes sold in Anambra State, south-eastern Nigeria

Abstract The levels of organochlorine and organophosphate pesticide residues in selected cereal crops (beans, cowpea, millet, maize, sorghum, and rice) purchased from major markets in Anambra, south-eastern Nigeria, were assessed and compared with established MRLs. The QuEChERS (quick, easy, cheap, effective, rugged, and safe) method was used for extraction and clean-up of pesticide residues. Thereafter detection and quantification were done using GC/MS. The result reveals that the analysed grain samples contained some organochlorine pesticides and organophosphates. The organochlorine was most dominant followed by the organophosphates. Organochlorine pesticide residues varied from 0.048 to 0.298 mg/kg in beans, BDL to 0.398 mg/kg in cowpea, 0.018–0.337 mg/kg in maize, 0.023–0.375 mg/kg in millet, 0.058–0.415 mg/kg in sorghum and 0.045–0.442 mg/kg in rice while organophosphate pesticide residue varied from BDL to 0.315 mg/kg in beans, BDL to 0.113 mg/kg in cowpea, BDL to 0.228 mg/kg in maize, BDL to 0.253 mg/kg in millet, BDL to 0.218 mg/kg in sorghum and BDL to 2.1 35 mg/kg in rice. Highest concentration of endosulphan II (0.442 mg/kg) was detected in rice, followed by aldrin (0.415 mg kg−1) in sorghum and endosulphan II (0.40 mg/kg) in sorghum. The pesticide toxicity index (PTI) was above one (1), whereas health index (HI) was less than one (1) and cancer risk were within USEPA reference guideline for crops indicating children will have greater health effect than adults. Hence, strict monitoring and control of pesticide residues in agricultural products is advocated.

Using the Pesticide Toxicity Index to show the potential ecosystem benefits of on-farm biobeds.

The influent and effluent of two single-cell biobeds (Province of Alberta, Canada) and two dual cell-biobeds (Province of Saskatchewan, Canada) were monitored during a number of growing seasons. A total of 59 unique pesticide active ingredients were detected, with all biobed influent samples (n=54) and 93% of effluent samples (n=54) containing pesticide mixtures. About one-half of the effluent samples in both single-cell (56%) and dual-cell (45%) biobeds contained active ingredients that have Groundwater Ubiquity Score (GUS) values >2.8 and so were more likely to move through the biomatrix materials into effluent. The Pesticide Toxicity Index (PTI) calculated for aquatic indicator species (i.e., vascular and nonvascular plants, invertebrates, and fish) was always larger for influent samples (e.g., median PTI>500 for invertebrates in dual-cell biobed) than effluent samples (i.e., median PTI<1). As such, this study demonstrates the potential ecosystem benefits of the broad adoption of on-farm biobeds in the Canadian Prairies for recycling tank rinsate as a strategy to accelerate a green economy. Although biobeds were highly effective in reducing the concentrations for pesticides with a wide range of soil organic carbon coefficient and half-life values, the biobed effectiveness was relatively poor for the herbicides clopyralid, diclofop, fluroxypyr, and imazethapyr. Clopyralid (3.02), fluroxypyr (3.70), and imazethapyr (3.90) all have relatively high GUS values(>2.8) and are thus more likely to be detected in effluent than active ingredients with smaller GUS values. This suggests that further improvements in biosystem design need to be made for optimizing the recycling of these pesticides.

Characterizing the exposure of streams in southern Ontario to agricultural pesticides

Aquatic communities can be exposed to pesticides transported from land. Characterizing this exposure is key to predicting potential toxic effects. In this study, samples of streamwater from 21 sites were used to characterize pesticide exposure to aquatic communities. Sites were in agricultural areas of southwestern Ontario, Canada and were sampled monthly from 2012 to 2019 from April to November. Samples were analyzed for a suite of hundreds of pesticides and pesticide degradation products and other water quality indicators (e.g., nutrients). Frequently detected pesticides included herbicides (2,4-D; bentazon; MCPP; metolachlor) and neonicotinoid insecticides (NNIs) (clothianidin; thiamethoxam) which were detected in >50% of samples collected between 2015 and 2019. Non-metric multidimensional scaling (NMDS) was used to explore connections between pesticide concentrations and upstream land use and crop type. Detectable concentrations of the NNI clothianidin and many herbicides were related to corn, soybean, and grain/cereal crops while concentrations of the NNI imidacloprid, insecticide flonicamid, and fungicide boscalid were related to greenhouse/nursery land use. Potential toxicity to aquatic communities was assessed by comparing pesticide concentrations to Pesticide Toxicity Index (PTI) values. Few samples exceeded levels where acute (1% of samples) or chronic toxicity (10.5%) would be expected. The diamide insecticide chlorantraniliprole was detected in several streamwater samples at levels that may cause toxicity to aquatic invertebrates, highlighting the need for continued toxicity research into this pesticide class. The number of pesticides detected was positively correlated with nutrient and total suspended solids levels, underscoring the multiple stressors aquatic communities are exposed to in these habitats.

Concentration of current-use pesticides in frogs from the Pampa region and correlation of a mixture toxicity index with biological effects

Contamination with current-use pesticides is frequently mentioned as a key factor in global amphibian declines although a limited number of studies have examined the mixture of pesticides accumulated by free-living frogs. This study examined the presence of 46 different pesticide residues in the muscle and kidney tissues of two frog species living in close association with row crops in the Pampa region of Argentina: The terrestrial Leptodactylus latinasus and the semi-aquatic Leptodactylus latrans. A total of 20 different pesticides were identified in frog tissues; chlorpyrifos-methyl, pirimiphos-methyl and acetochlor being the most frequently detected molecules. Overall, one or more pesticide residues (up to 12 in a single frog) were detected in 40–57 % of L. latrans. L. latinasus was found to present more pesticide detections than L. latrans. Interestingly, frog sampled in a natural reserve where no pesticides are applied presented an equivalent frequency of detections as frogs living near a crop. In L. latrans, the calculation of a pesticide toxicity index (PTI) permitted to highlight the existence of a strong positive correlation between PTI and liver GSH contents of females whereas, in males, PTI was negatively correlated with the perimeter of testicular seminiferous tubules. Males also presented near significant negative correlations between PTI and both body condition and the scaled fat index. These results indicate that frogs inhabiting agricultural regions are exposed to a complex and diffuse contamination by pesticide mixtures which is likely responsible for a number of biological effects that may be relevant at the population level.

Residential Proximity and Cumulative Risk Assessment of Agricultural Pesticide Applications in California

BACKGROUND AND AIM: Pesticide exposure based on residential proximity to agricultural applications has been associated with adverse health outcomes including developmental neurotoxicity such as reduced IQ and autism spectrum disorder, adverse birth outcomes such as low birth weight and birth defects as well as increased risk of cancer. However, epidemiological studies have primarily assessed individual pesticides or groups of pesticides sharing a common mechanism of action. In reality, individuals living near agricultural pesticide applications are exposed to a complex mixture of pesticides impacting a broad range of potential health harms. Here we develop a toxicity index for pesticide mixtures based on multiple chronic toxicity endpoints, and identify residential areas at greatest risk of adverse health outcomes due to pesticide exposure. METHODS: Data for pesticide applications were downloaded from the California Pesticide Use Reporting program (PUR). Over 400 active ingredients were assessed for chronic toxicity endpoints including carcinogenicity, neurotoxicity, endocrine disruption, thyroid toxicity and respiratory toxicity based on classifications from authoritative bodies including the EPA, IARC, and EFSA. We developed a toxicity index for each active ingredient based on the severity of the health outcome, the strength of the association, the reliability of the data source and the NOAEL if available. We then combined the toxicity index with application rates for all pesticides applied within a square mile. RESULTS:Pesticides with the greatest toxicity index include active ingredients previously associated with adverse health outcomes including organophosphates and carbamates. Other pesticides with high toxicity indices include neonicotinoids, pyrethroids and triazole fungicides. Residential areas of high risk of potential adverse health effects due to pesticide exposure from nearby agricultural applications were identified. CONCLUSIONS:Using the pesticide toxicity index and application rates in combination with residential proximity agricultural applications can help identify and prioritize high risk areas for future pesticide policy actions to best protect public health. KEYWORDS: pesticides, cumulative risk assessment, residential proximity

Pesticide Mixtures in the Water-Column Versus Bottom-Sediments of Prairie Rivers.

River water-column and bottom-sediments samples were screened for 160 pesticide compounds to compare the types of pesticides present in the water-column versus bottom-sediments, and between segments of rivers flowing through intensively-managed versus semi-natural habitats. Of the 35 pesticide compounds detected, current-use pesticides accounted for 96% (water) and 76% (bottom sediments). Pesticide mixtures were present in 72% (water) and 51% (sediment) of the total samples. Only the river flowing through the most intensively managed habitat showed a wide range of pesticides in sediments, and many of these pesticides were also present in the water-column of that river. Current-use fungicides were detected in both the water-column and bottom-sediments but not in samples taken from rivers flowing predominantly through semi-natural habitats. The study period (May to August) corresponds to the peak time of regional pesticide applications and hence the time period that is most likely to show elevated concentrations of current-use pesticides in the water-column. The environmental concentrations of pesticide mixtures detected in the water-column were used to calculate Pesticide Toxicity Index (PTI) values as it applies to non-vascular or vascular plants, invertebrates, and fish. The PTI values were largest for non-vascular and vascular plants, reflecting that the pesticide mixtures in water-column were dominated by herbicides.

Pesticide mixtures show potential toxicity to aquatic life in U.S. streams, water years 2013–2017

During water years (WY) 2013–2017, the U.S. Geological Survey, National Water-Quality Assessment (NAWQA) Project, sampled the National Water Quality Network – Rivers and Streams (NWQN) year-round and reported on 221 pesticides at 72 sites across the United States in agricultural, developed, and mixed land use watersheds. The Pesticide Toxicity Index (PTI) was used to estimate the potential chronic and acute toxicity to three taxonomic groups – fish, cladocerans, and benthic invertebrates. For invertebrates (either cladocerans, benthic invertebrates, or both), the maximum PTI score exceeded the predicted acute toxicity screening level at 18 of the 72 sites (25%) at some point during WY 2013–2017. The predicted toxicity of a single pesticide compound was found to overwhelm the toxicity of other pesticides in the mixtures after concentrations were toxicity weighted. For this study, about 71%, 72%, and 92% of the Fish-, Cladoceran-, and Benthic Invertebrate-PTI scores, respectively, had one pesticide compound primarily contributing to sample potential toxicity (>50%).There were 17 (13 insecticides, 2 herbicides, 1 fungicide, and 1 synergist) of the 221 pesticide compounds analyzed that were the primary drivers of potential toxicity in each water sample in which the PTI and TUmax (toxic unit score for the pesticide that makes the single largest contribution to the PTI) scores were above predicted chronic (>0.1) or acute (>1) toxicity levels for one of the three taxa. For cladocerans and benthic invertebrates, the drivers of predicted chronic (>0.1) and acute (>1) PTIs were mostly insecticides. For cladocerans, the pesticide compounds driving the PTI scores were bifenthrin, carbaryl, chlorpyrifos, diazinon, dichlorvos, dicrotophos, diflubenzuron, flubendiamide, and tebupirimfos. For benthic invertebrates, atrazine (an herbicide), as well as the insecticides – bifenthrin, carbaryl, carbofuran, chlorpyrifos, diazinon, dichlorvos, fipronil, imidacloprid, and methamidophos – were the drivers of predicted toxicity. For fish, there were three pesticide types that contributed the most to predicted chronic (>0.1) PTIs – acetochlor, an herbicide; carbendazim, a fungicide degradate; and piperonylbutoxide, a synergist.

Daily stream samples reveal highly complex pesticide occurrence and potential toxicity to aquatic life.

Transient, acutely toxic concentrations of pesticides in streams can go undetected by fixed-interval sampling programs. Here we compare temporal patterns in occurrence of current-use pesticides in daily composite samples to those in weekly composite and weekly discrete samples of surface water from 14 small stream sites. Samples were collected over 10-14weeks at 7 stream sites in each of the Midwestern and Southeastern United States. Samples were analyzed for over 200 pesticides and degradates by direct aqueous injection liquid chromatography with tandem mass spectrometry. Nearly 2 and 3 times as many unique pesticides were detected in daily samples as in weekly composite and weekly discrete samples, respectively. Based on exceedances of acute-invertebrate benchmarks (AIB) and(or) a Pesticide Toxicity Index (PTI) >1, potential acute-invertebrate toxicity was predicted at 11 of 14 sites from the results for daily composite samples, but was predicted for only 3 sites from weekly composites and for no sites from weekly discrete samples. Insecticides were responsible for most of the potential invertebrate toxicity, occurred transiently, and frequently were missed by the weekly discrete and composite samples. The number of days with benthic-invertebrate PTI ≥0.1 in daily composite samples was inversely related to Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness at the sites. The results of the study indicate that short-term, potentially toxic peaks in pesticides frequently are missed by weekly discrete sampling, and that such peaks may contribute to degradation of invertebrate community condition in small streams. Weekly composite samples underestimated maximum concentrations and potential acute-invertebrate toxicity, but to a lesser degree than weekly discrete samples, and provided a reasonable approximation of the 90th percentile total concentrations of herbicides, insecticides, and fungicides, suggesting that weekly composite sampling may be a compromise between assessment needs and cost.

Fate and Impact of Pesticides

Fate and Impact of Pesticides

Corrigendum to “Pesticide Toxicity Index—A tool for assessing potential toxicity of pesticide mixtures to freshwater aquatic organisms” [Sci. Total Environ. 476–477 (2014) 144–157

Corrigendum to “Pesticide Toxicity Index—A tool for assessing potential toxicity of pesticide mixtures to freshwater aquatic organisms” [Sci. Total Environ. 476–477 (2014) 144–157

Complex mixtures of dissolved pesticides show potential aquatic toxicity in a synoptic study of Midwestern U.S. streams

Aquatic organisms in streams are exposed to pesticide mixtures that vary in composition over time in response to changes in flow conditions, pesticide inputs to the stream, and pesticide fate and degradation within the stream. To characterize mixtures of dissolved-phase pesticides and degradates in Midwestern streams, a synoptic study was conducted at 100 streams during May–August 2013. In weekly water samples, 94 pesticides and 89 degradates were detected, with a median of 25 compounds detected per sample and 54 detected per site. In a screening-level assessment using aquatic-life benchmarks and the Pesticide Toxicity Index (PTI), potential effects on fish were unlikely in most streams. For invertebrates, potential chronic toxicity was predicted in 53% of streams, punctuated in 12% of streams by acutely toxic exposures. For aquatic plants, acute but likely reversible effects on biomass were predicted in 75% of streams, with potential longer-term effects on plant communities in 9% of streams. Relatively few pesticides in water—atrazine, acetochlor, metolachlor, imidacloprid, fipronil, organophosphate insecticides, and carbendazim—were predicted to be major contributors to potential toxicity. Agricultural streams had the highest potential for effects on plants, especially in May–June, corresponding to high spring-flush herbicide concentrations. Urban streams had higher detection frequencies and concentrations of insecticides and most fungicides than in agricultural streams, and higher potential for invertebrate toxicity, which peaked during July–August. Toxicity-screening predictions for invertebrates were supported by quantile regressions showing significant associations for the Benthic Invertebrate-PTI and imidacloprid concentrations with invertebrate community metrics for MSQA streams, and by mesocosm toxicity testing with imidacloprid showing effects on invertebrate communities at environmentally relevant concentrations. This study documents the most complex pesticide mixtures yet reported in discrete water samples in the U.S. and, using multiple lines of evidence, predicts that pesticides were potentially toxic to nontarget aquatic life in about half of the sampled streams.

Prediction of Pesticide Toxicity in Midwest Streams.

The occurrence of pesticide mixtures is common in stream waters of the United States, and the impact of multiple compounds on aquatic organisms is not well understood. Watershed Regressions for Pesticides (WARP) models were developed to predict Pesticide Toxicity Index (PTI) values in unmonitored streams in the Midwest and are referred to as WARP-PTI models. The PTI is a tool for assessing the relative toxicity of pesticide mixtures to fish, benthic invertebrates, and cladocera in stream water. One hundred stream sites in the Midwest were sampled weekly in May through August 2013, and the highest calculated PTI for each site was used as the WARP-PTI model response variable. Watershed characteristics that represent pesticide sources and transport were used as the WARP-PTI model explanatory variables. Three WARP-PTI models-fish, benthic invertebrates, and cladocera-were developed that include watershed characteristics describing toxicity-weighted agricultural use intensity, land use, agricultural management practices, soil properties, precipitation, and hydrologic properties. The models explained between 41 and 48% of the variability in the measured PTI values. WARP-PTI model evaluation with independent data showed reasonable performance with no clear bias. The models were applied to streams in the Midwest to demonstrate extrapolation for a regional assessment to indicate vulnerable streams and to guide more intensive monitoring.

Year-Round Monitoring of Contaminants in Neal and Rogers Creeks, Hood River Basin, Oregon, 2011-12, and Assessment of Risks to Salmonids.

Pesticide presence in streams is a potential threat to Endangered Species Act listed salmonids in the Hood River basin, Oregon, a primarily forested and agricultural basin. Two types of passive samplers, polar organic chemical integrative samplers (POCIS) and semipermeable membrane devices (SPMDs), were simultaneously deployed at four sites in the basin during Mar. 2011–Mar. 2012 to measure the presence of pesticides, polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs). The year-round use of passive samplers is a novel approach and offers several new insights. Currently used pesticides and legacy contaminants, including many chlorinated pesticides and PBDEs, were present throughout the year in the basin’s streams. PCBs were not detected. Time-weighted average water concentrations for the 2-month deployment periods were estimated from concentrations of chemicals measured in the passive samplers. Currently used pesticide concentrations peaked during spring and were detected beyond their seasons of expected use. Summed concentrations of legacy contaminants in Neal Creek were highest during July–Sept., the period with the lowest streamflows. Endosulfan was the only pesticide detected in passive samplers at concentrations exceeding Oregon or U.S. Environmental Protection Agency water-quality thresholds. A Sensitive Pesticide Toxicity Index (SPTI) was used to estimate the relative acute potential toxicity among sample mixtures. The acute potential toxicity of the detected mixtures was likely greater for invertebrates than for fish and for all samples in Neal Creek compared to Rogers Creek, but the indices appear to be low overall (<0.1). Endosulfans and pyrethroid insecticides were the largest contributors to the SPTIs for both sites. SPTIs of some discrete (grab) samples from the basin that were used for comparison exceeded 0.1 when some insecticides (azinphos methyl, chlorpyrifos, malathion) were detected at concentrations near or exceeding acute water-quality thresholds. Early life stages and adults of several sensitive fish species, including salmonids, are present in surface waters of the basin throughout the year, including during periods of peak estimated potential toxicity. Based on these data, direct toxicity to salmonids from in-stream pesticide exposure is unlikely, but indirect impacts (reduced fitness due to cumulative exposures or negative impacts to invertebrate prey populations) are unknown.

Changes in Pesticide Occurrence in Suburban Surface Waters in Massachusetts, USA, 1999–2010

Pesticide occurrence was determined in two suburban surface waters in eastern Massachusetts, USA during 2009 and 2010. Out of 118 collected samples, 45 samples showed detections of one or more target pesticides. Among the herbicides, 2,4-D was the most frequently detected and imidacloprid was the most frequently detected insecticide. Comparison with data from 1999 to 2000 indicated fewer pesticide detections and lower pesticide toxicity index values in the current study. Regulatory phaseout of chlorpyrifos and diazinon from residential use by 2004 was reflected in the results by the absence of chlorpyrifos detections and lower detection frequencies of diazinon. Detected pesticide levels were below aquatic life benchmarks.

Pesticide Toxicity Index—A tool for assessing potential toxicity of pesticide mixtures to freshwater aquatic organisms

Pesticide mixtures are common in streams with agricultural or urban influence in the watershed. The Pesticide Toxicity Index (PTI) is a screening tool to assess potential aquatic toxicity of complex pesticide mixtures by combining measures of pesticide exposure and acute toxicity in an additive toxic-unit model. The PTI is determined separately for fish, cladocerans, and benthic invertebrates. This study expands the number of pesticides and degradates included in previous editions of the PTI from 124 to 492 pesticides and degradates, and includes two types of PTI for use in different applications, depending on study objectives. The Median-PTI was calculated from median toxicity values for individual pesticides, so is robust to outliers and is appropriate for comparing relative potential toxicity among samples, sites, or pesticides. The Sensitive-PTI uses the 5th percentile of available toxicity values, so is a more sensitive screening-level indicator of potential toxicity. PTI predictions of toxicity in environmental samples were tested using data aggregated from published field studies that measured pesticide concentrations and toxicity to Ceriodaphnia dubia in ambient stream water. C. dubia survival was reduced to ≤50% of controls in 44% of samples with Median-PTI values of 0.1–1, and to 0% in 96% of samples with Median-PTI values >1. The PTI is a relative, but quantitative, indicator of potential toxicity that can be used to evaluate relationships between pesticide exposure and biological condition.

Parasitoid wasp diversity in apple orchards along a pest-management gradient

This study examined the impact of pest-management practices on Hymenopteran parasitoid diversity and assemblage composition in six apple orchards in southeastern Michigan, USA. The orchards comprised a gradient of pest-management intensity from organic to IPM to conventional practices. We used a pesticide toxicity index to quantify monthly and seasonal pest-management intensity in each orchard and conducted monthly vacuum-sampling of wasps during summer of 2009.Monthly toxicity scores predicted wasp abundance, setting an upper bound on the number of wasps in the orchard, but did not predict species richness. Total species richness was significantly higher in the organic orchard than in all others, but in August a conventional orchard had the highest wasp abundance and species richness. These results suggest that a toxicity index could guide pesticide choices or application times so as to increase parasitoid wasp populations, which have untapped potential for pest management in apple orchards.

Toxicity profile of labile preservative bronopol in water: The role of more persistent and toxic transformation products

Transformation products usually differ in environmental behaviors and toxicological properties from the parent contaminants, and probably cause potential risks to the environment. Toxicity evolution of a labile preservative, bronopol, upon primary aquatic degradation processes was investigated. Bronopol rapidly hydrolyzed in natural waters, and primarily produced more stable 2-bromo-2-nitroethanol (BNE) and bromonitromethane (BNM). Light enhanced degradation of the targeted compounds with water site specific photoactivity. The bond order analysis theoretically revealed that the reversible retroaldol reactions were primary degradation routes for bronopol and BNE. Judging from toxicity assays and the relative pesticide toxicity index, these degradation products (i.e., BNE and BNM), more persistent and higher toxic than the parent, probably accumulated in natural waters and resulted in higher or prolonging adverse impacts. Therefore, these transformation products should be included into the assessment of ecological risks of non-persistent and low toxic chemicals such as the preservative bronopol.

Comparison of pesticide concentrations in streams at low flow in six metropolitan areas of the United States

To examine the effect of urban development on pesticide concentrations in streams under low-flow conditions, water samples were collected at stream sites along an urban land use gradient in six environmentally heterogeneous metropolitan areas of the United States. In all six metropolitan areas, total insecticide concentrations generally increased significantly as urban land cover in the basin increased, regardless of whether the background land cover in the basins was agricultural, forested, or shrub land. In contrast, the response of total herbicide concentrations to urbanization varied with the environmental setting. In the three metropolitan areas with predominantly forested background land cover (Raleigh-Durham, NC, USA; Atlanta, GA, USA; Portland, OR, USA), total herbicide concentrations increased significantly with increasing urban land cover. In contrast, total herbicide concentrations were not significantly related to urban land cover in the three remaining metropolitan areas, where total herbicide concentrations appeared to be strongly influenced by agricultural as well as urban sources (Milwaukee-Green Bay, WI, USA; Dallas-Fort Worth, TX, USA), or by factors not measured in the present study, such as water management (Denver, CO, USA). Pesticide concentrations rarely exceeded benchmarks for protection of aquatic life, although these low-flow concentrations are likely to be lower than at other times, such as during peak pesticide-use periods, storm events, or irrigation discharge. Normalization of pesticide concentrations by the pesticide toxicity index -- an index of relative potential toxicity -- for fish and cladocerans indicated that the pesticides detected at the highest concentrations (herbicides in five of the six metropolitan areas) were not necessarily the pesticides with the greatest potential to adversely affect aquatic life (typically insecticides such as carbaryl, chlorpyrifos, diazinon, and fipronil).