Question of the Week
Answer: Acephate is a pesticide in the organophosphate family that is registered for use in the United States by the EPA. It has moderate persistence and has residual activity for approximately 15 days. It is used to control insect pests in agricultural and nursery crops by direct contact or ingestion.
Acephate has a half-life of three to six days and breaks down through microbial metabolism in the soil forming mostly CO2. However, another degradate is methamidophos, an organophosphate pesticide. Methamidophos is more toxic to mammals than is acephate, and breaks down to immobile compounds in about 20 days.
Both acephate and methamidophos are taken up and translocated in plants, from leaves to roots. Half-life disappearance in tobacco leaves, citrus fruit, greenhouse tomatoes, celery, and lettuce can range from 1 to 15 days. Produce sampled for residues has historically yielded 0.85 to 5.7% of samples having acephate residues, and 1.5 to 4.5% of samples having methamidophos residues. According to the Federal Registry, the acephate residue tolerance for most produce is between 0.1 to 0.3 ppm.
Studies by Chevron have shown that 14 to 18% of acephate remained in the soil after 20 days, and 0.27% was found in the soil during the whole 46-day test period. Leaching was seen to be the primary way acephate and methamidophos were removed from soil, with degradation happening 3 times faster in soils wetted to field capacity. These pesticides are very weakly adsorbed to soil particles, and has high mobility when the soils are subjected to heavy rainfall events.
Soil testing and testing labs
Two testing labs in California were identified from the ATTRA Alternative Soil Testing Laboratories database. Both of these labs have protocols for testing for pesticides:
Control Laboratories, Inc.
42 Hangar Way
Watsonville, CA 95076
Contact: Frank Shields, Mike Galloway
Control Laboratory, accumulated five decades of experience in analyzing and solving a wide spectrum of complex soil, soil-related, compost, and waterborne or effluent problems. Equipped with the finest state-of-the-art instrumentation and laboratory facilities, the company provides analytical services across the nation. These range anywhere from measurement and test of farm amendments and wastes to analysis of potential toxic substances.
AGQ Labs USA
2451 Eastman Ave. Suite 1
Oxnard, CA 93030
Contact: Jose Antonio Gomez
AGQ Labs USA is located in Oxnard California and specializes in two core sectors Agronomy and Food Safety. The lab is ISO/IEC 17025 accredited and provide following services Agronomy Services Soil Analysis Water Analysis Plant Tissue Analysis Agronomist/CCA Nutritional Monitoring GIS Mapping Golf Course Nutritional Management Food Safety Services Pesticide Residue Analysis MRL Compliance Mycotoxin Testing Heavy Metal Testing FDA Detentions Regulatory Assistance
Soils can be remediated by removing soil or adding clean soil and mixing it in with contaminated soil. This is often done on residential and industrial areas. However, for an agricultural field this is often neither feasible nor cost-effective. I recommend using an ecological method to remediate contaminated soils. Once you have a soil test and know the levels of acephate, you can plan a remediation method and monitor over time.
Bioremediation is a process of sequestering, destroying, or removing contaminants in soil using biological organisms. This can be done with plants (phytoremediation) or with microbes, or often a combination of both.
Most of the studies that have been done on specific plants and the fate of contaminants deal with heavy metals. However, some of the plants that are commonly used in phytoremediation of pesticides include annual mustards, brassicas, canola, willows, poplars, and warm season native grasses such as indiangrass. The ultimate fate of plant biomass grown on contaminated soil will depend on the mode of action (whether the contaminant is degraded or extracted into plant tissue). For instance, if contaminants are extracted, the plant biomass will need to be removed from the site.
The publication Phytoremediation: Protecting the Environment with Plants is one of the best treatments of the topic of all the resources available (see resources below). It provides information on phytoremediation and includes the various USDA-NRCS practice standards that can be used, with EQIP financial assistance, to establish plants for conservation purposes while also remediating contaminated soils. If you choose to plant a conservation cover crop or critical area planting (two of the many practice standards available), I recommend getting in contact with the NRCS conservationist in your area.
Resources for additional information
Phytoremediation: Protecting the Environment with Plants
Kansas State University
Acephate: Technical Fact Sheet
National Pesticide Information Center
Environmental Fate of Acetate
By Elizabeth Downing
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