Buried Horizon as record of organochlorine pesticides use in past time.

LUPI L; BEDMAR F; WUNDERLIN D.A; MIGLIORANZA, K.

Buenos Aires

Congreso; 11° Meeting SETAC-LatinAmerica; 2015

SETAC-LATINOAMÉRICA

Organochlorine Pesticides (OCPs) have been widely used as insecticides for crop treatment in Argentine. Currently the use of these compounds (such as p,p´-DDT, Endosulfans, Dieldrin, Chlordanes, HCHs, Heptachlors) have been banned at worldwide level, due to the long range transport capacity, high bioaccumulation properties, persistence in the environment and adverse effects to human health. Despite the legal restriction adopted for these contaminants, the residues can be found in the environment long time after the application in agricultural plots (AP) have occurred. They are usually associated with soil organic carbon content, considering the high hydrophobicity. On the other hand, in floodplains, where flow episodes are more usual, buried soils could be found. A flow episode occurred in 1980 in the proximity of Quequén River, changed the land topography of especially on the AP with large amounts of sand deposition. The objective of this work was determine pesticide levels in a buried horizon from an AP in relation to surface soil. Also, the AP contaminant levels were compared with a buffer zone near the river gully. OCPs were Soxhlet extracted and determined by GC-ECD. Results showed notable enrichment in organic carbon content (2 %) at 80-90 cm soil layer (buried horizon) from AP which decreased with depth, while surface soil (0-10 cm) showed lower organic carbon content (1.5 %). Total OCPs maximum concentration were 6 times higher in the buried horizon (2.2 ng g-1 d.w., 90-100 cm of depth) than in surface soil (0.4 ng g-1 d.w., 0-10 cm of depth) from AP. Also, a different distribution pattern in the concentration of groups was observed with depth (buried horizon: DDTs = Heptachlors > Endosulfans = g-HCH = Dieldrin > Chlordane while in surface soil: Endosulfans > DDTs > Heptachlors = g-HCH > Chlordane). The higher total OCPs concentration in the buffer zone was 0.6 ng g-1 d.w. (0-10 cm) and concentration from 45 cm to deeper layers were below 0.1 ng g-1 d.w. The group distribution pattern for the buffer zone was similar to surface soil from AP and Endosulfans were mainly found in deeper layers. These results suggest the possible presence of a buried agricultural soil and remark the importance of buried horizons in establishing a connection between past time and pesticide uses. Direct pesticide application in buried horizon and vertical transport should have contributed to the presence of these contaminants in the deepest soil layer from AP.