Glyphosate and AMPA concentrations in the respirable dust emitted experimentally by soil aggregates, shortly after herbicide application

Abstract

The objective of this study was to analyze glyphosate- and aminomethylphosphonic acid (AMPA) concentrations in the respirable dust (RD) emitted by different soil aggregates, shortly after herbicide application in a field approach. The relationships of both glyphosate and AMPA in the aggregates with organic matter- (OM), total iron- (Fe), and extractable phosphorus contents (P) as well as with pHCaCl2 values were analyzed. An Kastanozem haplic of the Semiarid Pampas (Argentina) was analyzed 7 days after glyphosate application. The RD (particulate matter < 10 mm in diameter, PM10) was generated and collected for the following aggregate-size fractions: < 0.42 mm, 0.42 to 0.84 mm, 0.84 to 2 mm, 2 to 6.4 mm, 6.4 to 19.2 mm, and > 19.2 mm. OM, P, Fe and pHCaCl2 were analyzed in the aggregate fractions, and glyphosate- and AMPA contents were measured both in RD and in the aggregate fractions. Glyphosate concentration varied between 16 mg kg−1 (aggregates < 0.42 mm) and 4.7 mg kg−1 (aggregates > 19.2 mm) and increased with decreasing size of the aggregates. Glyphosate concentration in RD varied between 48.5 mg kg−1 (aggregates < 0.42 mm) and 17.8 mg kg−1 (aggregates > 19.2 mm). Finest aggregates emitted RD with higher glyphosate concentrations. A positive relationship was determined between glyphosate in aggregates and glyphosate in RD (p < 0.05), indicating that aggregates with higher glyphosate concentration emitted a more glyphosate-enriched RD. Glyphosate in the aggregate fractions was not related to Fe, OM or pH of aggregates. Glyphosate- and P concentrations in aggregates were positively correlated. This is explained because both substances share a phosphonic acid functional group and they have similar reactivities in the soil. AMPA concentration varied between 130 mg kg−1 (aggregates > 19.2 mm) and 307 mg kg−1 (aggregates < 0.42 mm) in aggregates and between 527 ug kg−1 and 746 ug kg−1 in RD. AMPA concentrations in RD were not related to AMPA concentrations in aggregates. The contents of AMPA were higher than those of glyphosate in both, RD and aggregates, due to the longer persistence of AMPA in relation to glyphosate. In all cases, glyphosate- and AMPA concentrations were higher in RD than in the aggregates. Our results suggest that the RD emitted by agricultural soils has higher glyphosate- and AMPA concentrations than the bulk soil. These results encourage future investigations to elucidate if other pesticides (and the surfactants used in their formulations) are present in the RD emitted by agricultural soils. This information is necessary in order to evaluate the effects of the particulate matter emitted by agricultural soils on the whole ecosystem and the human health.