PhytoPharm · Phytotoxicological Risk of pharmaceuticals in soils

Phytotoxicological Risk of pharmaceuticals in soils

Population growth, urbanization, and climate change contribute to increasing stress on freshwater resources in many parts of the world. To address shortages, the reuse of wastewater has become increasingly valuable as an alternative source to meet irrigation demands. However, wastewater effluent is a known reservoir for pharmaceutical contaminants that enter the sewage system in urine and faeces after being poorly metabolised by the human body. Among the pharmaceuticals of most concern are antibiotics which have been shown to contribute to the proliferation of antibiotic resistance at low concentrations. Wastewater treatment facilities have historically been designed for the removal of excess nutrients as well as human pathogens. As a result, many emerging contaminants, including antibiotics, are poorly removed and enter the environment in treated wastewater effluent. When wastewater is used for irrigation, antibiotics can be introduced into the agroecosystem directly. Upon entry, these compounds partition between soil and porewater where they can be taken up into plants. As a result, these bioactive compounds have the potential to impact both plant health and soil microbial communities. The issue is further complicated by the fact that wastewater acts as a repository of all the antibiotics consumed by population mixed together. Antibiotics represent a set of molecules with diverse physicochemical properties as well as multiple modes of action, as a result, exposure to mixtures of antibiotics via the reuse of treated wastewater has the potential to threaten the sustainability of agricultural production as well as contribute to the proliferation of antibiotic resistance in the environment. Therefore, this project aimed to develop an algorithm to predict concentrations of antibiotics in treated wastewater based upon prescription and usage data. These results were then exploited to 1) predict hotspots of antibiotic resistance at the continental, national, and catchment scales, and 2) to provide an environmentally relevant mixture for use in a mesocosm study evaluating the impacts of antibiotic mixtures of plant growth and soil function. This work revealed that antibiotic exposure is dependent upon both prescription/usage as well as hydrologic processes that determine dilution. Using barley as a model crop due to its importance in the UK, we showed that exposure to an environmentally relevant mixture of 11 antibiotics had a negative impact on germination, but that overtime, mature plants showed few negative impacts as a result of routine antibiotic exposure. Microbial analysis revealed that continued exposure increased antibiotic resistance in native microbial communities and that genes associated with multi-drug resistance and beta-lactam resistance dominated. Continuous monitoring of CO2 gas fluxes revealed reductions in the net ecosystem exchange of CO2 with increased exposure in the soil-plant system. Overall, these results suggest that although wastewater reuse has become a valuable alternative to meet irrigation demands, risks associated with the exposure of antibiotics must be considered.

Data: CORDIS, © European Union