Pesticide Concentrations Associated with Augmented Flow Pulses in the Yolo Bypass and Cache Slough Complex, California

U.S. Geological Survey (USGS) | July 23rd, 2020

Surface-water and suspended-sediment samples were collected and analyzed by the U.S. Geological Survey for multiple current-use pesticides and pesticide degradates approx

Surface-water and suspended-sediment samples were collected and analyzed by the U.S. Geological Survey for multiple current-use pesticides and pesticide degradates approximately every 2 weeks at up to five sites in the Yolo Bypass and Cache Slough Complex before, during, and after augmented flow pulses in summer and fall 2016 and 2018 as well as during ambient flow conditions in summer and fall 2017 (no flow pulse). In 2016, augmented flows occurred during the summer (July) and required the pumping of Sacramento River water by local Reclamation Districts into the Colusa Basin Drain and Yolo Bypass Toe Drain. In contrast, augmented flows in 2018 occurred in the fall (August–September) and used agricultural tailwater (primarily rice field discharge water) to create the flow pulse. Water samples were analyzed by the U.S. Geological Survey for a suite of 175 current-use pesticides and pesticide degradates using gas chromatography with mass spectrometry and liquid chromatography with tandem mass spectrometry laboratory methods. Suspended sediments filtered from the water samples were analyzed for 143 pesticides and degradates by gas chromatography with mass spectrometry. During the study, 53 pesticides were detected, and all the samples contained mixtures of multiple pesticides at concentrations ranging from below method detection limits to 8,780 nanograms per liter. Pesticides used in growing rice were the dominant pesticides present at four of the five sites sampled and urban-use pesticides dominated at the remaining site. Overall, total pesticide concentrations tended to be higher at sites in the northern part of the Yolo Bypass and lower at southern sites, except for the farthest downstream site which received additional pesticide inputs from the Sacramento River. Flow-pulse water source influenced total pesticide concentrations in the Yolo Bypass and Cache Slough Complex, and the highest total pesticide concentrations at each site were detected either immediately before or during the flow pulse generated with agricultural tailwater in 2018. Data gathered during this study will aid the California Department of Water Resources and other agencies working in the region in adaptively managing pulse flows in the Yolo Bypass and Cache Slough Complex, as one of several California Natural Resources Agency’s Delta Smelt Resiliency strategies.

Pesticide inputs to the Sacramento–San Joaquin Delta, 2015–16: Results from the Delta Regional Monitoring Program

U.S. Geological Survey (USGS) | July 11th, 2018

Emergent hypotheses about causes of the pelagic organism decline in the Sacramento–San Joaquin Delta (Delta) indicate that a more complete understanding of the quality

Emergent hypotheses about causes of the pelagic organism decline in the Sacramento–San Joaquin Delta (Delta) indicate that a more complete understanding of the quality of water entering the Delta is needed. Less than half of all pesticides used in the Delta watershed are measured in samples collected for routine monitoring, and with new pesticides continually being registered for use, the concentrations of unmonitored pesticides in the Delta ecosystem are unknown. In response, a multi-year, cooperative effort to improve monitoring of mercury, nutrients, pathogens, and pesticides was begun by the Delta Regional Monitoring Program (RMP). In July 2015, the U.S. Geological Survey in cooperation with the Delta RMP began measuring concentrations of 154 pesticide compounds in monthly samples of surface water and suspended sediment collected at five major inputs to the Sacramento–San Joaquin Delta from July 2015 to June 2016. In addition to pesticide concentration measurements, field water-quality indicators (water temperature, specific conductance, dissolved oxygen, pH, and turbidity) were measured at each site and samples were collected for the analysis of dissolved organic carbon, dissolved copper, particulate organic carbon, particulate inorganic carbon, total particulate carbon, and total particulate nitrogen. Pesticide concentrations in particulates were measured in collected suspended-sediment samples by gas chromatography with mass spectrometry, whereas concentrations measured in surface-water samples utilized a combination of gas chromatography with mass spectrometry and liquid chromatography with tandem mass spectrometry. Samples were collected from two sites in the San Joaquin River watershed and at one site for each of the Mokelumne River, Sacramento River, and Ulatis Creek watersheds. All water samples contained mixtures of 2–25 pesticides. Pesticides were detected in 100 percent of surface-water samples. A total of 54 pesticide compounds were detected in water samples during the study period (19 fungicides, 18 herbicides, 9 insecticides, 7 breakdown products, and 1 synergist). The most frequently detected pesticide compounds were the herbicides hexazinone (95 percent) and diuron (73 percent) and the fungicides boscalid (93 percent) and azoxystrobin (75 percent). Pesticide concentrations ranged from below the method detection limits to 2,630 nanograms per liter for the herbicide metolachlor. A total of 11 pesticide compounds were detected in the suspended sediments filtered from water samples (6 herbicides, 3 insecticides, 1 fungicide, and 1 breakdown product). The most frequently detected compounds were the insecticides permethrin (7 percent) and bifenthrin (5 percent) and the herbicide pendimethalin (5 percent). Pesticide concentrations in the suspended-sediment ranged from below the method detection limit to 265 nanograms per liter for the herbicide pendimethalin.

Pesticide Mixtures in the Sacramento–San Joaquin Delta, 2016–17: Results from Year 2 of the Delta Regional Monitoring Program

U.S. Geological Survey (USGS) | December 6th, 2019

Pesticides in fog

Nature Portfolio (Springer Nature) | February 18th, 1987

The discovery of the very acidic nature of fog and clouds1,2 has created much interest in sampling, analysing, and elucidating the chemistry of fog, principally because a

The discovery of the very acidic nature of fog and clouds1,2 has created much interest in sampling, analysing, and elucidating the chemistry of fog, principally because an understanding of the chemical transformations leading to acid fog may provide important clues to the origin of acid rain. Recently, the knowledge of the chemistry of fog has expanded to include carbonyl compounds3, volatile organic acids4, and alkyl sulphonates5,6. We have discovered that a variety of pesticides and their toxic alteration products are present in fog, and that they occasionally reach high concentrations relative to reported rainwater concentrations. In our experiments, we were able to measure the air–water distribution coefficients of pesticides between the liquid fog and the interstitial gas phase. These measurements reveal that some chemicals are enriched several thousandfold in the suspended liquid fog droplets compared to equilibrium distributions expected from Henry's Law coefficients for pure aqueous solutions.

Pesticides in the Nation’s Streams and Ground Water, 1992–2001

U.S. Geological Survey (USGS) | February 28th, 2006

This report is one of a series of publications, The Quality of Our Nation’s Waters, that describe major findings of the NAWQA Program on water-quality issues of regiona

This report is one of a series of publications, The Quality of Our Nation’s Waters, that describe major findings of the NAWQA Program on water-quality issues of regional and national concern. This report presents evaluations of pesticides in streams and ground water based on findings for the first decadal cycle of NAWQA. “Pesticides in the Nation’s Streams and Ground Water, 1992–2001” greatly expands the analysis of pesticides presented in “Nutrients and Pesticides,” which was the first report in the series and was based on early results from 1992 to 1995. About 1 billion pounds of conventional pesticides are used each year in the United States to control weeds, insects, and other pests. The use of pesticides has resulted in a range of benefits, including increased food production and reduction of insect-borne disease, but also raises questions about possible adverse effects on the environment, including water quality. The NAWQA assessment of pesticides provides the most comprehensive national-scale analysis to date of pesticide occurrence and concentrations in streams and ground water. NAWQA results show where, when, and why specific pesticides occur in streams and ground water across the Nation, and yield science-based implications for assessing and managing the quality of our water resources.

Quality of Groundwater Used for Domestic Supply in the Modesto, Turlock, and Merced Subbasins of the San Joaquin Valley, California

U.S. Geological Survey (USGS) | January 6th, 2023

More than 2 million Californians rely on groundwater from privately owned domestic wells for drinking-water supply. This report summarizes a water-quality survey of domes

More than 2 million Californians rely on groundwater from privately owned domestic wells for drinking-water supply. This report summarizes a water-quality survey of domestic and small-system drinking-water supply wells in the Modesto, Turlock, and Merced subbasins of the San Joaquin Valley where more than 78,000 residents are estimated to use privately owned domestic wells. Results indicate that inorganic and organic constituents in groundwater were respectively present above regulatory (maximum contaminant level, MCL) benchmarks for public drinking-water quality in 37 percent and 9 percent of the aquifer area used for domestic drinking-water supplies (herein, “domestic groundwater resources”). The most prevalent inorganic constituents exceeding regulatory benchmarks were nitrate, uranium, and arsenic. The only organic constituents exceeding regulatory benchmarks were the fumigant constituents 1,2,3-trichloropropane (1,2,3-TCP) and 1,2-dibromo-3-chloropropane (DBCP), but the herbicides atrazine and simazine were detected at low concentrations below one-tenth of regulatory benchmarks in 30 percent of domestic groundwater resources. Total dissolved solids (TDS) and manganese exceeded aesthetic-based (secondary maximum contaminant level [SMCL]) benchmarks for drinking water in 3 percent and 13 percent of domestic groundwater resources, respectively. Per- and polyfluoroalkyl substances (PFAS) were detected in 23 percent of domestic groundwater resources, with 4 percent exceeding California state notification or response levels for specific compounds. Total coliform bacteria were detected in 20 percent of domestic groundwater resources. Elevated concentrations of nitrate, uranium, TDS, and pesticides (fumigant constituents and herbicides) are related to agricultural land use and were typically present at shallow depths up to 75 meters below land surface. Agriculturally derived constituents were detected in wells screened below the Corcoran Clay Member of the Tulare Formation (herein, “Corcoran Clay”) in the southeastern part of the study area, where the Corcoran Clay tends to be shallower and thinner than in areas to the northwest. Nitrate, uranium, and TDS were most prevalent in the northwest part of the study area proximal to the valley trough where soils are poorly drained and agricultural land uses are predominantly grain, alfalfa, and dairy farms. Pesticides tended to occur in groundwater below coarse-grained surficial deposits and within a northwest to southeast trending band along the eastern extent of the Corcoran Clay that typically demarcates the western extent of well-drained soils associated with perennial orchard crops. Elevated concentrations of arsenic tended to occur west of this band in reducing groundwater but also sometimes co-occurred with elevated nitrate in oxic groundwater, most likely because of geochemical conditions in agriculturally affected groundwater that can enhance the mobility of arsenic from aquifer sediments.

Regional nitrate and pesticide trends in ground water in the eastern San Joaquin Valley, California

American Society of Agronomy (ASA) | September 18th, 2008

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this stu

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this study, spatial and temporal trends in concentrations of nitrate and pesticides in ground water in the eastern San Joaquin Valley, California, were evaluated to determine the long-term effects of agricultural and urban development on regional ground-water quality. Trends in concentrations of nitrate, the nematocide 1,2-dibromo-3-chloropropane, and the herbicide simazine during the last two decades are generally consistent with known nitrogen fertilizer and pesticide use and with the position of the well networks in the regional ground-water fl ow system. Concentrations of nitrate and pesticides are higher in the shallow part of the aquifer system where domestic wells are typically screened, whereas concentrations are lower in the deep part of the aquifer system where public-supply wells are typically screened. Attenuation processes do not seem to significantly affect concentrations. Historical data indicate that concentrations of nitrate have increased since the 1950s in the shallow and deep parts of the aquifer system. Concentrations of nitrate and detection of pesticides in the deep part of the aquifer system will likely increase as the proportion of highly affected water contributed to these wells increases with time. Because of the time of travel between the water table and the deep part of the aquifer system, current concentrations in public-supply wells likely reflect the effects of 40- to 50-year-old management practices.

Salinity Changes the Dynamics of Pyrethroid Toxicity in Terms of Behavioral Effects on Newly Hatched Delta Smelt Larvae

Toxics (MDPI) | February 20th, 2021

Salinity can interact with organic compounds and modulate their toxicity. Studies have shown that the fraction of pyrethroid insecticides in the aqueous phase increases w

Salinity can interact with organic compounds and modulate their toxicity. Studies have shown that the fraction of pyrethroid insecticides in the aqueous phase increases with increasing salinity, potentially increasing the risk of exposure for aquatic organisms at higher salinities. In the San Francisco Bay Delta (SFBD) estuary, pyrethroid concentrations increase during the rainy season, coinciding with the spawning season of Delta Smelt (Hypomesus transpacificus), an endangered, endemic fish. Furthermore, salinity intrusion in the SFBD is exacerbated by global climate change, which may change the dynamics of pyrethroid toxicity on aquatic animals. Therefore, examining the effect of salinity on the sublethal toxicity of pyrethroids is essential for risk assessments, especially during the early life stages of estuarine fishes. To address this, we investigated behavioral effects of permethrin and bifenthrin at three environmentally relevant concentrations across a salinity gradient (0.5, 2 and 6 PSU) on Delta Smelt yolk-sac larvae. Our results suggest that environmentally relevant concentrations of pyrethroids can perturb Delta Smelt larvae behavior even at the lowest concentrations (<1 ng/L) and that salinity can change the dynamic of pyrethroid toxicity in terms of behavioral effects, especially for bifenthrin, where salinity was positively correlated with anti-thigmotaxis at each concentration.

Simulations of Ground-Water Flow and Particle Pathline Analysis in the Zone of Contribution of a Public-Supply Well in Modesto, Eastern San Joaquin Valley, California

U.S. Geological Survey (USGS) | July 1st, 2008

Sustainable Cotton Project

San Francisco Estuary Institute (SFEI) | November 19th, 2009

Contamination from pesticide application to row crops is a major water quality issue in California. Cotton receives three to five times greater application of pesticide p

Contamination from pesticide application to row crops is a major water quality issue in California. Cotton receives three to five times greater application of pesticide per acre than other row crops (USGS 2008). This Project included outreach, education, and technical support for growers to test alternatives to synthetic pesticides and inorganic fertilizers. In addition, water quality monitoring of cotton field runoff in the Central Valley of California was conducted during the 2007 and 2008 growing seasons. The goal of the study was to evaluate differences in pesticide and nutrient loads to receiving water bodies comparing biological and conventional growing practices. The types and concentrations of pesticides in the sampled tail water were similar for biologically and conventionally grown cotton. Average pesticide concentrations in water and estimated loads for diuron, glyphosate, chlorpyrifos, and prometryn were not statistically significantly different with BMP implementations at the biological sites due to sample size limitations. However, there was a trend toward lower pesticide concentrations for diuron and prometryn at the biological sites. Concentrations for most nutrient forms and loads were also generally similar within the two site types when compared to flow passing the site at the point of sampling. Nitrate and nitrite loads, however, were reduced at the biological fields by more than 70% compared to the conventional sites. Additionally, limited bioassessment samples showed slightly greater numbers of individuals and numbers of species collected at the biological sites.