Organochlorine Pesticides in agricultural soils and their relationship with surficial and growndwater pollution of the Rio Negro Basin, Patagonia, Argentina

MIGLIORANZA KARINA SILVIA BEATRIZ; GONZALEZ MARIANA; ONDARZA PAOLA MARIANA; SHIMABUKURO VALERIA; ISLA FEDERICO I; PEÑA ARANZAZU; AIZPUN JULIA ELENA; MORENO VICTOR JORGE

New Orleans, Louisiana, USA

Congreso; 30th SETAC North America Annual Meeting. Human-Environmental Interactions: Understanding Change in Dynamic Systems; 2009

SETAC

Organochlorine pesticides (OCPs) are ubiquitous contaminants which occurrence in the environment is of special concern because of their persistence, toxicity and ubiquity. The Negro river watershed is the main fruit production of Argentina settled at the north of Patagonia area with an important history of high agrochemicals use. The environmental fate of pesticides in soils is of concern due to the problems resulting from of mobility and persistence of chemicals leading to deterioration of surface waters and groundwater quality. Monitoring of organochlorine pesticides was carried out to identify and quantify the contribution of point and nonpoint sources to the total OCPs flux in the Negro river watershed. Moreover desorption of pesticides were studied in order to evaluate the potential risk of surficial and groundwater contamination. Soils profiles were taken in the surround along the river, and different depths were analyzed for organic matter content, particles size distribution and contaminants levels. OCPs such as HCHs, DDT and its metabolic products, alpha and beta-Endosulfan and its metabolite sulfate, were determined by GC-ECD. Desorption was assessed by adding surfactants mixtures (SDS/Tw80) or dissolved organic matter from humic acids or sewage sludge using batch experiments. The higher total OCPs levels (1315 ng/g dry weight) were found in surface soils (0-5cm) from the Upper Valley, main fruit production zone. Moreover a high correlation to organic matter content was observed for the most samples. A predominance of DDTs (1275 ng/g dry wt, 80% DDE) followed by Endosulfan sulfate (18 ng/g dry wt) denote the importance of the  legacy of forbidden pesticides and those from recent use, respectively. When the profiles was evaluated a decreasing gradient of total pesticides was found concomitantly with depth. The other profiles, upstream (49 ng/g dry wt) and downstream (1.1 ng/g dry wt), showed a similar pattern but with lower total pesticide levels. Surfactant mixtures (SDS 2 cmc-4 cmc) resulted in an enhanced solubilisation, mainly p,p’-DDE (200 fold greater than control). Dissolved organic carbon from sewage sludge increased also desorption 1-2 times while with humic acids was higher. Caution should be taken if this contaminated soils were irrigated with waters, from different sources, containing surfactants or humic acids, because it would lead to enhanced desorption and mobilization of hydrophobic contaminants such as DDE reaching finally surficial or groundwater.