Studies concerning the fate of atrazine and chlorpyrifos in a biobased pesticide waste disposal system

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Virginia Tech

A disposal system for pesticide waste was examined for the ability to isolate waste pesticides onto lignocellulosic matrices, such as peat moss (PM) or steam-exploded wood fibers (SEW) by sorption processes, and to detoxify the pesticide during solid state fermentation (SSF) in contained bioreactors.

Emulsions formed from typical pesticide formulations acts as a barrier for pesticide sorption. Adding Ca(OH)₂ for demulsification ofDursban® 4E and filtering suspended particulates was the most effective steps for decreasing chlorpyrifos concentration. Activated carbon (AC) and rubber (R) were better at sorbing chlorpyrifos than the PM and SEW, even though the two sorbents were capable of removing approximately 95% chlorpyrifos from solution. Secondary columns of AC or R could be employed to further remove chlorpyrifos or similar pesticides from the waste water.

Atrazine and chlorpyrifos dissipation in field SSF bioreactors increased with higher bioreactor temperatures (65 °C). Dissipation time for 50% parent compound disappearance (DT₀) of atrazine in 1 m³, cylindrical (1 m diameter), and plastic bag (189L) bioreactors were 2, 14, and days, respectively. The chlorpyrifos DT₀ values for the same bioreactors were 59, 20, and 50 days, respectively. Chlorpyrifos did not volatilize outside the compost as expected, but was found condensed in the cooler outer regions of the bioreactor matrix.

Supplemental energy and fertilizer sources (com meal, vegetable oil, and chicken manure) enhanced microbial activity and pesticide degradation in field bioreactors. The dissipation of atrazine was not enhanced by nutrient amendment in laboratory studies involving ¹⁴C-radiolabeled atrazine and chlorpyrifos at 40 °C over 16 weeks. The DT₀ values were 4 weeks for nutrient amended and unamended bioreactors. Nutrient amendment increased chlorpyrifos dissipation with DT so values of approximately 11 and 17 weeks for nutrient and unamended bioreactors but not in the atrazine bioreactors.

Dissipation of chlorpyrifos was mainly through volatility and degradation, whereas atrazine dissipated by degradation and unextractably associated with the matrix. It is important to keep pesticide waste bioreactors well aerated, moist, and mixed with additions of nitrogen and fresh biomass to facilitate the dissipation and detoxification of pesticides. The remaining residue can be land applied, land filled, or incinerated.

compost, pesticide waste, sorption, mites, atrazine, chlorpyrifos