Organic Micropollutants from an Agricultural Drainage Ditch Contaminate a Shrimp Farm in Sinaloa (Mexico)

Among nutrients and pesticides, agricultural draining ditches also transport pollutants discharged with untreated wastewater from the municipalities adjoining the ditch. When the ditch water is used for irrigation and aquaculture, risks for the environment and food production are suggested. For the conducted field study, a shrimp farm in Sinaloa (Mexico) was used to trace organic pollutants (pesticides and pharmaceutical residues) on their way from an agricultural draining ditch to a shrimp farm fed partially by the drain water. The concentrations of pollutants in the drain water ranged from 10 ng L-1 to 453 ng L-1. The pond water of the shrimp farm contained concentrations between <10 ng L-1 and 177 ng L-1. The shrimps were contaminated by pollutants at concentrations between 40 μg kg-1 d.w. (dry weight) to 3.3 mg kg-1 d.w. (fungicide Metalaxyl). Health risks for the cultivated shrimps cannot be excluded because some pesticides are known for their toxic effects to crustaceans. The concentrations of selected antibiotics in the shrimps were low and comparable with those found in the shrimps declared as seawater shrimps from a German supermarket. The incorporation of the antibiotics was probably caused by contact to the wastewater in the shrimp ponds and/or by contaminated shrimp feed. Additionally to the anthropogenic chemicals, coliforms were determined in the water (total coliforms: 30-50 CFU 100 mL-1; fecal coliforms: 0-20 CFU 100 mL-1). These values agree with the Mexican Norm NOM-242-SSA1-2009 representing a microbiological quality of water adequate for aquaculture. The number of coliforms measured in shrimp was higher than in pond water, suggesting bioaccumulation and a potential health risk for consumers.