ARS | Publication request: Sorption of triazine and organophosphorus pesticides on soil and biochar

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 6, 2012
Publication Date: March 6, 2012
Citation: Uchimiya, M., Wartelle, L.H., Boddu, V.M. 2012. Sorption of triazine and organophosphorus pesticides on soil and biochar. Journal of Agricultural and Food Chemistry. 60(12):2989-2997.

Interpretive Summary: Environmental fate of agrochemicals is complex, and is controlled by sorption and degradation in soils. Chemical structure of the pesticide controls how fast and how far the sorption and degradation proceed, depending on the soil property (organic matter, clay, and other mineral contents). This study provides a useful information for predicting the fate of different agrochemicals in soils as well as biochar, a soil amendment used to enhance agricultural production. Agrochemicals (malathion, parathion, diazinon, and deisopropylatrazine) were irreversibly sorbed on soils and biochars. Some agrochemicals suppressed the sorption of another agrochemical on soils. Biochars having high surface area were able to sorb as much as half of its own weight of agrochemicals. These results will allow producers to predict both efficacy and runoff contamination risk of different agrochemicals, and utilize biochars for a long-term pesticide management practice on farm.

Technical Abstract: Although a large number of reports are available on sorption and degradation of triazine and organophosphorus pesticides in soils, systematic studies are lacking to directly compare and predict the fate of agrochemicals having different susceptibilities for hydrolysis and other degradation pathways. This study investigated the sorption-desorption isotherms and kinetics for triazine (deisopropylatrazine) and organophosphorus (malathion, parathion, diazinon) pesticides on clayey, acidic and weathered Puerto Rican valley soil, heavy metal contaminated small arms range (SAR) soils of sandy and peaty nature, as well as selected biochars having a wide range of BET surface areas (4.7-2,061 mg g-1). On the valley soil, malathion sorption did not reach equilibrium for 3 wk, suggesting more irreversible sorption (likely involving covalent binding on soil components) compared to diazinon and deisopropylatrazine (that are more likely to bind via weaker, e.g., cation exchange mechanism). For both triazine and organophosphorus pesticides, greater sorption was observed on a peaty SAR soil containing 16-fold higher total organic carbon, compared to the sandy SAR soil. On SAR soils, deisopropylatrazine competed with the sorption of diazinon and malathion, while neither diazinon nor malathion competed with deisopropylatrazine. Hysteresis was observed for both diazinon and deisopropylatrazine on SAR soils. Comparison of solution-phase phosphorus and malathion concentrations suggested the binding of phosphorus-containing degradation products on soil surfaces. Prolonged contact with SAR soils also resulted in the degradation of diazinon and an increase in soluble phosphorus concentrations. The following general increasing trend was observed for the sorption on different soil samples: deisopropylatrazine < malathion < diazinon < parathion. Sorption of a stable and least sorbing compound, deisopropylatrazine, was highly hysteric on cottonseed hull biochars prepared at 350 and 800 oC, and was dramatically enhanced by higher BET surface areas of biochars resulting from higher pyrolysis temperature and by steam and KOH activations.