Monitoring for Pesticides

Jan. 19, 2012

A prominent red dot in northern California, on the United States Geological Survey (USGS) map of the US, draws attention to the situation at Arcade Creek in Sacramento. The map shows concentrations of organophosphate insecticides in the nations urban waterways (Domagalski et al. 2000). According to the USGS National Water-Quality Assessment project, which had been studying the creek since 1994, “Diazinon levels at the urban stream, Arcade Creek, were elevated at various times of the year and exceeded recommended criteria for the protection of aquatic life for every measurement taken [emphasis added]. Those levels were among the highest in the nation.”

Since the mid-1990s, based on data from their own monitoring and that of state, federal, and academic investigators, stormwater agencies throughout California have been faced with frequent and widespread toxicity in urban waterways caused by legal applications of insecticides currently registered by EPA. Although the local agencies are legally accountable for this toxicity under provisions of their National Pollutant Discharge Elimination System (NPDES) permits, their ability to effectively address this toxicity using their own legal authority is extremely limited. Federal law establishes pesticide use requirements through enforceable labels (“the label is the law”), and similar to many states, California law preempts control of pesticide use by local agencies. Although local agencies could theoretically enforce stormwater discharge limitations against pesticide applicators and even property owners, the practical and political implications of that are clearly daunting.

Among our responses to pesticide toxicity were development of programs to promote integrated pest management (IPM) and including, where necessary, the use of pesticides with less water-quality and overall environmental impact. Wastewater and stormwater agencies in the Bay Area, in conjunction with the Bio-Integral Resource Center (BIRC), developed Our Water Our World, which promotes water-friendly, least-toxic products and IPM practices, and provides staff training and point-of-sale information for retail stores. In Sacramento, the stormwater programs worked with the University of California IPM program to develop a similar program called WaterWise. Both of these programs have spread statewide. In addition to consumer-oriented programs, stormwater programs have supported my participation in the development of EcoWise and GreenPro, which are IPM certification programs for structural pest control companies. We’ve gotten the California Structural Pest Control Board to adopt regulations to allow truthful marketing of IPM programs and require IPM training for pest management licensees, and to explore adoption of standards for IPM certification programs.

Experience with public education campaigns to promote reduced pesticide use through IPM indicates that these efforts will be insufficient on their own to prevent aquatic toxicity caused by widely used insecticides. Because washoff of only a very small proportion of applied material is necessary to cause toxicity, even a 25% reduction in insecticide application achieved by a public outreach campaign (which would generally be considered a wildly successful effort) would be unlikely to prevent toxicity. In addition, public outreach campaigns are pitted against aggressive and well-funded marketing efforts by manufacturers to encourage pesticide use, and against the reasonable expectations among the public and pest control industry that legally available pesticides will meet the federal standard of not causing undue environmental harm if used according to label restrictions.

During the ’90s, our analysis of state pesticide laws and pesticide regulatory authority under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) indicated that both the California Department of Pesticide Regulation (CDPR), and EPA’s Office of Pesticide Programs (OPP) had the authority and legislative mandate to evaluate and regulate pesticides in a manner that prevented urban water-quality impacts. However, historically both agencies have focused on agricultural uses, so urban uses received less rigorous scrutiny, despite calculations (based on the state’s sales and use data) that show at least half of all pesticide use occurring in urban areas. A partnership of California water-quality agencies–including publicly owned treatment works (POTWs); local stormwater agencies; and even the state and regional water boards that administer Clean Water Act provisions such as NPDES permits, water-quality standards, and total maximum daily loads (TMDLs)–have been consistently pressing pesticide regulators on this issue, and in recent years there has been significant cooperation and progress made toward more effective regulation of pesticides.

The problem of urban pesticide aquatic toxicity came to light in the early years of the stormwater program, when as part of their NPDES monitoring programs, local stormwater agencies in California began to conduct toxicity bioassays on urban runoff and in receiving waters. These tests revealed that runoff and urban creeks often had acute toxicity to the invertebrate Ceriodaphnia dubia, a standard freshwater test species. Chemical analyses and toxicity identification evaluations (TIEs) revealed the culprits to be the insecticides diazinon and chlorpyrifos.

Monitoring data showed diazinon and chlorpyrifos in urban waterways at concentrations of generally around 0.5 to 1.0 parts per billion (ppb), although sometimes much higher. While on their face these seem like miniscule amounts, these values are actually quite high when compared to the known toxicity values for these compounds. Diazinon and chlorpyrifos are extremely toxic to insects and other arthropods, including crustaceans found in receiving water ecosystems and used as standard test species, like Daphnia spp, Ceriodaphnia dubia, and various shrimp and amphipods. For Ceriodaphnia, the chlorpyrifos LC50 is about 80 parts per trillion (0.080 ppb), and the diazinon LC50 is about 300 to 500 parts per trillion (0.3 to 0.5 ppb). (The LC50, or lethal concentration 50, is the concentration of a chemical which kills 50% of a sample population.) As a result, water-quality objectives established by the state to protect aquatic species in California’s Central Valley were set for diazinon at 0.080 ppb (acute, 1-hour average) and 0.050 ppb (chronic, 4-day average), and for chlorpyrifos at 0.020 (acute, 1-hour average) and 0.014 ppb (chronic, 4-day average).

At the time, these pesticides, part of the organophosphate class of insecticides, were very commonly applied in the urban areas where the toxicity occurred. In 1996, DPR data, based on pesticide use reports required from professional applicators, indicated that in Sacramento County alone, over 35,000 pounds of chlorpyrifos and 10,000 pounds of diazinon (as active ingredient, not formulated product) were applied by professional applicators for structural pest control. Similar rates of structural applications were evident all over the state. The vast majority of these applications would have been in urban areas. According to industry representatives, a significant portion of these applications would have been applied as an outdoor perimeter spray around buildings, but much of it would also have been used as a subsurface termite application, which is much less likely to impact water quality. While non-professional applications of pesticides are not reported, statewide sales data, combined with known reported uses, indicate that amount of these pesticides sold annually to retail customers is generally about the same as annual reported usage, at least within an order of magnitude.

The combination of large volumes applied, coupled with impervious urban surfaces and highly toxic properties, meant that less than 1% of the material applied in a typical urban watershed needed to run off to cause the actual concentrations observed through monitoring. In addition, to test the assertion by some stakeholders that toxicity was being caused by illegal dumping, a detailed study of an urban subwatershed was conducted. This study showed pesticides at remarkably uniform concentrations at numerous locations, a finding more consistent with widespread runoff from legal uses rather than a patchy distribution indicative of isolated dumping.

Under the Clean Water Act, the water boards began establishing numeric diazinon and chlorpyrifos water-quality objectives and TMDLs for impacted water bodies and inserting pesticide provisions in municipal separate storm sewer system (MS4) and POTW permits. Local agencies began to establish in-house programs to reduce pesticide use, develop programs to promote IPM among the public and industry, and conduct additional chemical and toxicity monitoring. These activities have been very expensive for both the state and local agencies, with aggregate statewide costs running into many millions of dollars. The state water board estimates that the development of one TMDL for an impacted water body costs the state approximately $600,000. Even more staggering are implementation costs born by stormwater programs: The San Francisco Bay regional board estimated in its TMDL report that the implementation cost for the pesticide-related TMDL for Bay Area urban creeks would be roughly $7 million annually (Johnson 2005).

Photo: USGS
Map of concentrations of organophosphate insecticides in the nation’s urban waterways

Monitoring costs for local agencies are a big part of the equation: TIE costs begin at about $8,500 each, which in some cases may be required for each bioassay toxicity hit. In response to toxicity caused by pyrethroid insecticides (which replaced diazinon and chlorpyrifos) in fiscal year 2006–07, Riverside County in southern California incurred monitoring costs of approximately $1 for each of the 275,000 residents of the watershed being regulated.

Understanding that local actions alone would not stop pesticide toxicity or prevent liability for potential Clean Water Act violations, and that ongoing compliance costs would be burdensome, California water-quality agencies began to take deliberate action to affect state and federal pesticide regulations. A group of stakeholders that called itself the Urban Pesticide Committee began meeting in the mid-1990s on a regular basis to share information and discuss potential strategies for preventing aquatic pesticide toxicity in urban waters. A 1999 letter to EPA Administrator Carol Browner from the Stormwater Quality Task Force (the predecessor of the California Stormwater Quality Association, or CASQA) outlined our concerns and implored EPA to prevent urban water-quality impacts through its FIFRA authority. The Diazinon and Pesticide-Related Toxicity TMDL for San Francisco Bay Area Urban Creeks, prepared by the regional board, included the language “Gaps in pesticide regulatory programs . . . result in discharges that adversely affect urban creek water quality.” The Sacramento Stormwater Quality Partnership adopted a formal pesticide plan that specifically identified local agency activity to promote changes in state and federal pesticide regulatory policy as a key component of complying with its MS4 permit.

In a stroke of luck for California stormwater programs, the EPA OPP took action under the Food Quality Protection Act to remove from registration virtually all urban uses of diazinon and most urban uses of chlorpyrifos, which took full effect by 2004 for diazinon and 2005 for chlorpyrifos. Although the primary driver for this action was the reduction of exposure of children to these potent neurotoxins, the observed improvements in water quality in urban areas were striking: All over California, the regulation of diazinon and chlorpyrifos by OPP caused the rapid elimination of almost all instances of toxic concentrations of these insecticides in urban receiving waters. The few ongoing excursions above water-quality objectives may be associated with ongoing use of stockpiled materials or, in the case of chlorpyrifos, with the few types of applications still allowed in urban areas.

Unfortunately, this happy ending was really just another beginning. One pesticide problem was about to be replaced by another. Residents and businesses still had a lot of Argentine ants, the most common general pest of urban areas in California. The public and pest management professional (PMPs) alike turned to pyrethroids to control them. As predicted by a 2003 insecticide market trends analysis conducted by Dr. Kelly Moran on behalf of the water boards and the San Francisco Estuary Project, applications of pyrethroid insecticides rapidly increased in urban areas, rising from 380,000 pounds of active ingredient in 2000 to 850,000 pounds in 2006, a more than twofold increase. Pyrethroids were attractive because of relatively low mammalian toxicity, high residual toxicity to target organisms, and the belief that their affinity to soil and sediment particles would prevent them from having significant water-quality impacts. Unfortunately, water-quality impacts occurred anyway.

Photo: Dr. Erin Amweg, UC Berkeley
“Urban drool”: Overwatering can wash pesticides into storm drains.

In 2004, Dr. Don Weston, a University of California, Berkeley, professor specializing in ecotoxicology, began finding significant toxicity impacts of pyrethroids on urban creeks and rivers in the Bay Area and Sacramento regions. Much of the observed toxicity associated with pyrethroids has been to the sediment dwelling amphipod Hyalella azteca, an EPA standard toxicity test organism. Hyalella is a common inhabitant of California urban waterways, so the toxicity has real-world significance to urban stream ecology. Disturbingly, pyrethroid toxicity has also been observed in the water column and is not limited to Hyalella, having been observed in other arthropod test organisms by other investigators. CASQA conducted a review of pyrethroid chemical and toxicity monitoring studies by academic researchers, stormwater agencies, the state water board, and DPR that showed toxic levels of pyrethroids and pyrethroid-associated toxicity in urban water bodies throughout California. Sampling locations were screened to exclude or isolate the effects of agricultural pyrethroid uses. Widespread pyrethroid toxicity has resulted in initiation of a formal “reevaluation” of pyrethroids by DPR and in a continuing significant level of interest among California water agencies. The re-evaluation is also addressing the concerns of POTWs, because effluent toxicity has been found at several wastewater treatment plants.

Now that pyrethroids are a known water-quality problem, replacement products for the structural pest control market are also of concern to California water agencies. Fipronil, for example, has great potential to degrade water quality and is also known to be recently increasing in reported uses for structural pest control. For a variety of reasons, this insecticide is becoming more popular among pest management professionals for Argentine ant control, and even though its use is just beginning to ramp up, water-quality monitoring data are already showing fipronil occurring in some urban waterbodies at concentrations approaching toxic levels.

The rapid replacement of organophosphate toxicity by pyrethroid toxicity, and the beginnings of yet another problem with fipronil as it is beginning to supplant pyrethroids, highlights the need to get ahead of the curve in regulating pesticides that can impact water quality. The Clean Water Act is largely a reactive statute: Once a problem is identified, it imposes penalties and restrictions on dischargers. These mechanisms can kick into place without regard to the ability of the discharger to control the pollutant source. Dischargers have to spend a lot of money, and are under threat of enforcement actions and third-party lawsuits.

Stormwater agencies are in an especially difficult position because they are regulated as point-source dischargers under the NPDES program, although they frequently have little control over what are essentially nonpoint-source pollutants located throughout their service areas. Pesticides in stormwater are especially problematic because many are toxic at extremely low concentrations Their removal from stormwater to below toxic levels would be unattainable by typical affordable stormwater treatment systems. Outdoor pesticides, copper from brakes, and zinc from tire treads, are all examples of nonpoint-source pollutants in widely used products that are not well controlled by local action and are better addressed by regulations on product use and content. In contrast to the Clean Water Act, FIFRA has a number of mechanisms that are intended to be used proactively to identify and mitigate potential water-quality and other environmental impacts of pesticides before they are released to the market.

As mentioned above, OPP’s and DPR’s historical focus on agricultural pesticides have left their regulation of urban pesticides lagging behind, at least with respect to water-quality protection. In the last decade, CASQA and other California water quality agencies have made a concerted effort to work with these two agencies to improve the situation, and significant progress has been made. The overall thrust has been to get OPP and DPR to work more closely with local, state, and federal water agencies to shift from reacting to problems to proactively preventing pesticide-related toxicity and compliance problems. Simple enough in concept, but both agencies have a lot of inertia and moving parts, and it takes a long time for them to change how they conduct their business.

Some of the discussion has been on big-picture items: getting the pesticide regulators to recognize the nature and scope of the problem, incorporating into the risk-assessment process a better understanding of how pollutants move through the urban environment, adjusting data submittal requirements for manufacturers, and considering the regulatory and financial implications for the local agencies when balancing the risks and benefits of pesticide uses.

Other work has revolved around the tools used to evaluate aquatic toxicity. Ironically, the methods used by OPP to evaluate water-quality impacts of pesticides are not consistent with the methods used by the Office of Water (OW) to establish water-quality standards. A key difference has been the use of test organisms with very different sensitivities. If OPP uses data on a less-sensitive species as the basis for its aquatic risk assessment, there is a good chance that it will underestimate the likelihood of water-quality impacts that have regulatory implications to dischargers. Daphnia species (often used for OPP risk assessments) are about 10 times less sensitive than Ceriodaphnia and a hundred times less sensitive than Hyalella to pyrethroids. This is extremely important to water-quality agencies, because water-quality criteria, which are levels of contaminants established by OW to be protective of water quality, often form the basis of designating impaired water bodies and establishing numeric limits.

Happily, largely in response to concerns expressed (and data submitted) by California water-quality agencies, OPP and DPR have made a number of significant improvements in response to our concerns. OPP and OW are now engaged in a rigorous and ongoing effort to “harmonize” their methods for characterizing water-quality effects of pesticides. OPP has “front-loaded” pyrethroids into its 15-year registration review cycle and is incorporating mandatory mitigation measures on pyrethroid labels designed to reduce urban water-quality problems. DPR placed pyrethroids into official “reevaluation” status and is in the process of adopting surface water protection regulations that will apply to pyrethroids used by licensed applicators. OPP is beginning to require data from manufacturers that will better support aquatic risk assessments in urban environments.

The improvements made by OPP and DPR, while important and greatly appreciated, were the fruit of a lot of effort by California water agencies. Countless hours of analysis and review of regulatory documents were necessary to generate numerous comment letters and to work with OPP and DPR staff directly through conference calls, one-on-one discussions, and stakeholder meetings. In 2005, CASQA’s Pesticide Subcommittee was formed to focus on these issues and to provide EPA with specific detailed and often highly technical comments on its regulatory actions. I have been appointed by EPA to OPP’s Pesticide Program Dialogue Committee, and by DPR to its Pest Management Advisory Committee, which have become important venues for influencing these agencies to commit more resources to addressing urban pesticide and pest management issues. Dr. Moran’s leadership and hard work on behalf of water-quality agencies have been heroic: She has led the analysis of pesticide impacts, regulations, and risk assessments and has facilitated critical communication and data sharing among stakeholders. Overall, these efforts over the last decade or so have accomplished a much greater level of understanding and collaboration among the water-quality agencies, DPR, and OPP.

A very important improvement we’d still like to see is for pesticide regulators to consider pesticide use patterns as part of the regulatory process, instead of focusing on individual chemicals or chemical classes. The primary reason is the need to analyze the potential for new water-quality problems to arise as regulatory changes spur shifts from one chemical (or class) to a new chemical (or class). For instance, we can already the see shifts we predicted in the chemicals used (OP to pyrethroid to fipronil) for Argentine ant control around structures. We’d like to see OPP and DPR go through similar steps to anticipate likely market shifts within a use pattern, and get ahead of the game by establishing science-based mitigation measures before water-quality problems emerge.

Another change we’d like to see is consideration of the availability of practical and effective pest management alternatives as part of the registration process. In the FIFRA world, when making registration decisions, OPP is supposed to weigh both the impacts and the benefits of the chemical. If effective, non- or least-toxic alternatives to a particular chemical are available, the benefit/impact ratio of using the chemical is diminished, and more restrictive mitigation measures can be more readily justified. This concept actually came into play recently with metaldehyde, a very common snail bait. Very effective, least-toxic iron phosphate baits and non-toxic cultural controls were readily available. Mitigation measures for metaldehyde included labeling that promoted cultural controls and required strong warnings (including graphics) regarding hazards to children and pets. One of the ancillary benefits of stormwater program involvement in developing and promoting IPM programs is that they can help demonstrate the effectiveness and availability of alternative control measures.

Dr. Les Greenberg, UC Riverside
Insecticide applications to impervious surfaces can be easily mobilized in urban runoff.

This article highlights pesticide issues in California, but lest stormwater managers in other regions get too comfortable, they might want to take a look at some of the other red dots on USGS map. The concentrations of diazinon and chlorpyrifos likely have diminished in these areas since urban uses of these chemicals were mostly curtailed nationwide, but in a more recent USGS study pyrethroids have been detected in urban water bodies of Atlanta, GA; Boston, MA; Dallas/Fort Worth, TX; Denver, CO; Milwaukee/Green Bay, WI; Salt Lake City, UT; and Seattle/Tacoma, WA. A 2009 study by Hintzen, Lydy, and Belden focused on urban streams in central Texas and found significant levels of pyrethroid toxicity there.

On the horizon, we’re looking for ways for OPP and DPR to institutionalize the changes we’ve sought, so that each registration incorporates the types of analyses necessary to prevent problematic levels of pesticides in urban waterways. There are hundreds of pesticides that will eventually go through registration review. Careful screening will reveal those that have the potential to impact urban creeks and rivers and need additional evaluation (and potentially mitigation measures). As local agencies, we’d like to get out of the business of improving pesticide regulation and be able to rely on OPP and DPR to protect our urban waterways as a normal course of business.

Domagalski, J. L., D. L. Knifong, P. D. Dileanis, L. R. Brown, J. T. May, V. Connor, and C. N. Alpers. 2000. Water Quality in the Sacramento River Basin, California, 1994–98. US Geological Survey Circular 1215. Available online at

Hintzen, E. P., M. J. Lydy, and J. B. Belden. 2009. “Occurrence and Potential Toxicity of Pyrethroids and Other Insecticides in Bed Sediments of Urban Streams in Central Texas.” Environmental Pollution 157(1):110-6.

Johnson, B. 2005. Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks. Water Quality Attainment Strategy and Total Maximum Daily Load (TMDL). Final Staff Report. Prepared by the California Regional Water Quality Control Board, San Francisco Bay Region. November 9. Available online at

Further Resources
Detailed reports about regulatory activities, monitoring, and science relevant to pesticides in urban runoff are available at the UP3 Project website run by the San Francisco Estuary Partnership:

Certified structural IPM services significantly reduce the risk of insecticides in urban runoff. GreenPro ( ) and Green Shield ( ) are national programs. EcoWise ( ) is available in California.

Our Water Our World ( ) is great example of a program that involves stormwater agencies partnered with local and big box retailers throughout California. 
About the Author

Dave Tamayo

Dave Tamayo is a supervising environmental specialist with the Sacramento County Stormwater Program where he has worked for 16 years. He co-chairs the CASQA Pesticides Subcommittee, serves as the county IPM coordinator, is vice president of the California Structural Pest Control Board, and is a graduate student in entomology at the University of Florida.

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Photos courtesy Chino Basin Water Reclamation District.
From left: Matt Hacker, Metropolitan Water District of Southern California; Marco Tule, Inland Empire Utilities Agency Board President; Gil Aldaco, Chino Basin Water Conservation District Board Treasurer; Curt Hagman, San Bernardino County Supervisor; Elizabeth Skrzat, CBWCD General Manager; Mark Ligtenberg, CBWCD Board President; Kati Parker, CBWCD Board Vice President; Teri Layton, CBWCD Board member; Amanda Coker, CBWCD Board member.