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Chapter 26
Best Management Practices for Mitigating Pesticides in Runoff from Vegetable Systems in California Michael D. Cahn*,1 and Bryn Phillips2 1University
of California, Cooperative Extension, Monterey County, 1432 Abbott Street, Salinas, California 93901, United States 2Department of Environmental Toxicology, University of California, Davis, Granite Canyon Laboratory, 34500 Highway 1, Monterey, California 93940, United States *E-mail:
[email protected].
Commercially produced vegetables in California utilize a variety of pesticides to prevent losses from insects, diseases, and weeds. Several classes of these chemicals have been shown to impair water quality in receiving water bodies by causing toxicity and impacts to resident benthic macroinvertebrate communities. Common pesticide compounds have a wide range of solubilities and can vary greatly in how long they persist in the environment. Toxicity tests using a variety of aquatic organisms and field assessments of in-stream invertebrate populations demonstrate the potential for acute and chronic pesticide impacts in receiving waters. State and local regulators have encouraged growers to reduce the amount pesticides in runoff through source control and the installation of on-farm management practices that treat runoff. This chapter introduces strategies for source control and summarizes the most common types of on-farm management practices. Treatment practices are roughly grouped by their ability to remove hydrophobic and soluble compounds from agricultural runoff and can be further characterized by the main mitigation strategies: infiltration, degradation, sorption, and sedimentation. Integrated approaches show the most promise
© 2019 American Chemical Society Goh et al.; Pesticides in Surface Water: Monitoring, Modeling, Risk Assessment, and Management ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
for maximizing reduction of pesticide loading and associated toxicity to aquatic organisms.
Pesticide Use in Vegetable Production in California Vegetables are widely grown throughout California, representing $7.8 billion annually in agricultural sales (1), and are produced on approximately 1 million acres (2). Warm season vegetables such as tomatoes, peppers, onions, and melons are grown in the central valleys (Sacramento and San Joaquin), inland coastal valleys (Santa Clara, San Benito), and the southern desert regions of California (Coachella and Imperial). A majority of the cool season vegetables, including leafy greens such as lettuce and spinach and cole crops such as broccoli, cauliflower, and kale are produced in the coastal valleys (Pajaro, Salinas, Santa Maria, and Oxnard), where the climate generally has moderate air temperatures throughout the year. Cool season vegetables are also produced in the desert region during the winter and in the San Joaquin valley during the spring and fall. Vegetables from California are sold across the United States and are exported to continents throughout the world including the Americas (Canada and Mexico), Asia (Japan, China, Taiwan), and Europe (European Union) (3). Consistent with most crops produced commercially, pesticides are used in vegetables to prevent yield loss from insect pests, weeds, and diseases. Insects can reduce yield through direct feeding on leaves, fruits, and roots or indirectly by introducing viruses that affect crop growth. Quality standards required for vegetables are strict. The presence of insects as well as markings and discolorations caused by insects can render a crop unmarketable. Lettuce, for example, will not be harvested if aphids are present inside the heads at maturity. Processing tomatoes cannot be canned as whole peel products if the surface of the fruit is discolored from stink bug feeding. Viruses introduced by aphid feeding on honeydew melons can discolor the epidermal layer of the fruit and result in an unmarketable product. Spotted wilt virus that is introduced to peppers and tomatoes through the feeding of thrips can cause large blotches to appear on the fruit. Several classes of pesticides used to control insects in vegetables have been shown to impair water quality in California, including organophosphates, pyrethroids, and neonicotinoids. Laboratory (4) and field (5) tests have demonstrated that these pesticides cause toxicity to aquatic organisms, and have been linked to impacts on benthic macroinvertebrate communities in receiving water systems (6, 7). Based on their partitioning coefficients (Table 1), these pesticide classes range in solubility from extremely soluble (neonicotinoids) to hydrophobic (pyrethroids) and have varying environmental persistence. Neonicotinoids have very short half-lives in water when exposed to light, whereas pyrethroids can persist in water and soil for months to years. Organisms used in laboratory toxicity tests have a range of sensitivities to these chemical classes. For example, the cladoceran Ceriodaphnia dubia is most sensitive to organophosphates, the amphipod Hyalella azteca is most sensitive to pyrethroids, and the midge Chironomus dilutus is most sensitive to neonicotinoids (8). 520 Goh et al.; Pesticides in Surface Water: Monitoring, Modeling, Risk Assessment, and Management ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
Table 1. Chemical Properties and Half-Lives of Pesticides in Three Classes Class Organo-phosphate
Pyrethroid
521
Neo-nicotinoid
x
Log Kocx
Log Kowy
Chlorpyrifos
3.8
Diazinon
Chemical
Water Half Life (Days)
Soil Half Life (Days)
Hydrolysis
Photolysis
Aerobic
4.7
58
25
64
2.3
3.8
138
Stable
38
Malathion
2.5
2.8
6
