Hazard prioritization and risk characterization of antibiotics in an irrigated Costa Rican region used for intensive crop, livestock and aquaculture farming.

Antibiotics alter the homeostasis of microbial communities and select for antibiotic-resistant bacteria in the wild. Thus, the accumulation of unnaturally high concentration of these substances in the environment due to their use in human activities can be regarded as a neglected form of pollution, especially in countries with agricultural-based economies. Qualitative and quantitative information on antibiotic usage in Costa Rica is scarce, hence the design and enforcement of prevention strategies and corrective measures is difficult. To address this issue, and aiming in the long run to contribute with a more rational use of pharmaceuticals in the tropics, we characterized the hazard associated with the antibiotics used during 2008 in agriculture, aquaculture, pig farming, veterinary medicine and human medicine in the major irrigation district of Costa Rica. Hazard indicators were calculated based on antibiotic use and a weighted algorithm that also considered antibiotic fate, toxicity, and resistance. Moreover, hazard quotients were computed using maximum environmental concentrations reported for Costa Rican surface waters and predicted no effect concentrations for aquatic organisms. The number of antibiotics used in the ATID during the study were n = 38 from 15 families. Antibiotic consumption was estimated at 1169-109908 g ha year and, distinctively, almost half of this figure was traced back to phenicols. Tetracyclines, with a particular contribution of oxytetracycline, were the most widely used antibiotics in agriculture and veterinary medicine. Oxytetracycline, florfenicol, chlortetracycline, sulfamethoxazole, erythromycin, ciprofloxacin, enrofloxacin, sulfamethazine, trimethoprim and tylosin, in that order showed the highest hazard indicators. Moreover, hazard quotients greater than 1 were calculated for oxacillin, doxycycline, oxytetracycline, sulfamethazine, and ciprofloxacin. Studies dealing with the ecotoxicology of tetracyclines, sulfonamides and quinolones, as well as surveys of phenicol resistance among environmental bacteria, should be prioritized in Costa Rica.