24
Sep
U.S. Geological Survey Finds Mixtures of Pesticides Are Widespread in U.S. Rivers and Streams
(Beyond Pesticides, September 24, 2020) A new report by the U.S. Geological Survey (USGS), National Water-Quality Assessment (NAWQA) Project, reveals the presence of pesticides is widespread in U.S. rivers and streams, with over almost 90 percent of water samples containing at least five or more different pesticides. Pesticide contamination in waterways is historically commonplace as a 1998 USGS analysis revealed pesticides are commonly found in all U.S. waterways, with at least one pesticide detectable. Thousands of tons of pesticides enter rivers and streams around the U.S. from agricultural and nonagricultural sources, which contaminate essential drinking water sources, such as surface water and groundwater. As the number of pesticides in waterways increases, it has detrimental impacts on aquatic ecosystem health, especially as some pesticides work synergistically with others to increase the severity of the effect. Reports like these are a significant tool in determining appropriate regulatory action to protect human, animal, and environmental health. USGS concludes, “Identification of primary contributors to toxicity could aid efforts to improve the quality of rivers and streams to support aquatic life.”
Water is the most abundant and important chemical compound on earth, essential to survival and the main component of all living things. Less than three percent of that water is freshwater, and only a fraction of that freshwater is groundwater (30.1%) or surface water (0.3%) readily available for consumption. However, ubiquitous pesticide use threatens to reduce the amount of available freshwater as pesticide runoff, recharge, and improper disposal tends to contaminate adjacent waterways, like rivers, streams, lakes, or underground watersheds. With rivers and streams only accounting for 2% of surface waters, it is essential to protect these vulnerable ecosystems from further degradation, including aquatic biodiversity loss, a decrease in water quality/drinkability. Researchers in the report note, “[The] primary objective of this study was to characterize pesticide mixtures found in stream water samples at 72 sites across the United States in watersheds with agricultural, developed, and mixed land uses during 2013–2017.” Additionally, researchers aim to understand the “potential toxicity to aquatic life from the pesticide mixtures and evaluate the occurrence of drivers of potential mixture toxicity.”
To assess national water quality, researchers collected water samples from watershed sampling sites established in 1992 by the National Water Quality Network (NWQN) – Rivers and Streams, based on land-use type (agricultural, developed/urban, and mixed). From 2013-2017, researchers collected water samples from each watershed site monthly, increasing collection frequency in months with greater pesticide runoff, like rainy seasons. Researchers assessed pesticide levels in water samples using direct-aqueous injection liquid chromatography with tandem mass spectrometry to analyze a total of 221 pesticide compounds in filtered (0.7 μm) water samples at the USGS National Water Quality Laboratory. To evaluate pesticide toxicity, researchers applied a Pesticide Toxicity Index (PTI) to measure the potential toxicity of pesticide mixtures to three taxonomic groups – fish, cladocerans (small freshwater crustaceans), and benthic invertebrates. PTI score classification encompasses three levels to represent approximate screening levels of predicted toxicity: low (PTI ≤ 0.1), chronic (0.1 < PTI ≤1), and acute (PTI > 1).
The results find that during 2013-2017 at least five or more pesticides present in 88% of water samples from NWQN sampling sites. Only 2.2% of the water samples have no pesticide concentrations above detectable levels. The median number of pesticides present per water samples from each land-use type is highest in agricultural settings with 24 pesticides, and lowest in mixed (both agricultural and developed land) settings with seven pesticides. Developed areas fall in the middle, amassing 18 pesticides per water sample. Pesticides in water samples are potentially acutely to chronically toxic to aquatic invertebrates and chronically toxic to fish. Of the 221 pesticide compounds analyzed, 17 (13 insecticides, two herbicides, one fungicide, and one synergist) are primary drivers of toxicity in aquatic taxonomic groups. According to the PTI analysis, one pesticide compound contributes to >50% of the sample toxicity, while other present pesticides only contribute minimally to toxicity. For cladocerans, the main pesticide compounds driving toxicity are the insecticides bifenthrin, carbaryl, chlorpyrifos, diazinon, dichlorvos, dicrotophos, diflubenzuron, flubendiamide, and tebupirimfos. The herbicide atrazine and the insecticides bifenthrin, carbaryl, carbofuran, chlorpyrifos, diazinon, dichlorvos, fipronil, imidacloprid, and methamidophos are the main drivers of potential pesticides toxicity for benthic invertebrates. Pesticides that have the most chronic impact on fish include the herbicide acetochlor, the fungicide degradant carbendazim, and the synergist piperonylbutoxide.
The U.S. Geological Survey (USGS) “assesses the occurrence and behavior of pesticides in streams, lakes, and groundwater and the potential for pesticides to contaminate our drinking-water supplies or harm aquatic ecosystems,” via its National Water-Quality Assessment (NAWQA) reports. Previous USGS reports demonstrate that pesticides are ubiquitous in the aquatic environment and a pervasive contaminant of freshwater ecosystems. Many of the most commonly used pesticides in the U.S. are detectable in both surface and groundwater, which serve as drinking water sources for half of the U.S. population. Furthermore, pesticide-contaminated rivers and streams can discharge polluted water into oceans and lagoons like the Great Barrier Reef (GBR), where a mixture of over 20 different pesticides are present in 99.8% of GBR samples. However, these chemicals can have adverse health impacts, not only on aquatic organisms but terrestrial organisms which rely on surface or groundwater. Many of these chemicals cause endocrine disruption, reproductive defects, neurotoxicity, and cancer in humans and animals, and most are highly toxic to aquatic species. Additionally, water quality surveys usually detect the presence of more than one pesticide compound in waterways and the possible toxicity on marine organisms. However, neither USGS-NAWQA nor EPA’s aquatic risk assessment evaluates the risks a mixture of pesticides can pose to the aquatic environment.
Pesticide contamination in surface and groundwater raises another issue of deficient waterway monitoring and regulations that allow pesticides to accumulate in waterways. One of the ways the U.S. Environmental Protection Agency (EPA) protects human and environmental health is by regulating pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and point source pollution in waterways as sanctioned by the Clean Water Act. However, EPA’s recent rollbacks on waterway regulations do little to protect aquatic ecosystem health, which marine, and terrestrial species, including humans, require. Previously, USGS-NAWQA has criticized EPA for not establishing sufficient water quality benchmarks for pesticides. According to NAWQA, “Current standards and guidelines do not completely eliminate risks posed by pesticides in waterways because: (1) values are not established for many pesticides, (2) mixtures and breakdown products are not considered, (3) the effects of seasonal exposure to high concentrations have not been evaluated, and (4) some types of potential effects, such as endocrine disruption and unique responses of sensitive individuals, have not yet been assessed.”
The results of the study demonstrate 17 different pesticides are primary drivers of aquatic toxicity. Organophosphate insecticides are most responsible for chronic cladoceran toxicity, while imidacloprid insecticides cause chronic toxicity in benthic invertebrates. Organophosphates are a class of insecticides know to have adverse effects on the nervous system, having the same mode of action as nerve agents for chemical warfare. Exposure to imidacloprid insecticides can have adverse effects on the reproductive system and are highly toxic to various aquatic species. Although dichlorvos, bifenthrin, and methamidophos are rarely present within samples, when these chemicals are present, they exceed chronic and acute toxicity thresholds for aquatic invertebrates. However, researchers state toxicity indexes could underestimate the potential impact on aquatic life as past research finds that “short-term, potentially toxic peaks in pesticides frequently are missed by weekly discrete sampling.”
Aquatic invertebrates, including benthic organisms and cladocerans, are an essential part of the food web, consuming excess nutrients in the water, as well as being a food source for larger predators. However, the effects of pesticide contamination in waterways can have a bottom-up influence on the aquatic invertebrates, killing off beneficial invertebrates whose nerve system is similar to the terrestrial insect targets. Additionally, many benthic invertebrates are larvae of terrestrial insects, which are not only indicators of waterway quality and biodiversity but provide various ecosystem services such as bio-irrigation, decomposition, and nutrition. It is essential to mitigate the impacts that potentially toxic pesticides have on aquatic organisms in rivers and streams by regulating pesticide inputs, especially in regions where agrochemical use is more widespread.
The report reveals the number of pesticides in samples varied annually by site, with agriculture sites bearing the highest levels of pesticide use, including herbicides, insecticides, and fungicides, with severe seasonal influxes from May-July. Midwestern and Southern regions have the highest median number of pesticides per water sample due to the abundance of agricultural land use. These findings are consistent, with previous research suggesting water sources near agricultural regions tend to have higher levels of contaminants, especially during springtime, when agrochemical runoff is more rampant. A February 2020 USGS reporting on a collaborative sampling project (conducted with EPA) for pesticides in waterways detected 141 pesticides in seven Midwest streams and 73 in seven streams in the Southeast. Already, the Trump Administration waives the requirement of the multinational chemical company Syngenta-ChemChina to continue monitoring Midwest waterways for the presence of the weedkiller atrazine through 2020. Additionally, the administration’s replacement of the 2015 Waters of the United States (WOTUS) rule with the Navigable Waters Protection Rule will significantly weaken the protection of several U.S. waterways and wetlands, and by forsaking prohibitions on activities that threaten waterways from a variety of pollution harms. As the implications of climate change worsen, increasing instances of rainfall, and thus runoff, as well as glacial ice melt, which entraps legacy pesticides no longer in production, lack of specific pesticide monitoring can cause toxic chemicals to accumulate and synergize in the aquatic environment, further polluting water sources.
The use of pesticides should be phased out and ultimately, eliminated to protect the nation’s and world’s waterways and reduce the number of pesticides that make their way into your drinking water. Additionally, Beyond Pesticides has long advocated for protective federal regulation that considers potential synergistic and additive threats, to ecosystems and organisms, from admixtures of pesticides — whether in formulated products or “de facto” in the environment. Unfortunately, current administration regulations fail to consider the environment holistically, thus creating a blind spot that limits our ability to enact widespread change that truly improves ecosystem health. However, advocating for local and state pesticide reform policies can protect you and your family from pesticide-contaminated water. Furthermore, organic/regenerative systems conserve water, nurtures fertility, reduces surface runoff and erosion, reduces the need for nutrient input, and critically, eliminates the toxic chemicals that threaten so many aspects of human and ecosystem life, including water resources. For more information about pesticide contamination in water, see the Threatened Waters program page and Beyond Pesticides’ article Pesticides in My Drinking Water? Individual Precautionary Measures and Community Action. Tell the U.S. Environmental Protection Agency that it must do its job to protect health and the environment.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: USGS Press Release, USGS Report
