Environmental and public health related risk of veterinary zinc in pig production - Using Denmark as an example

At great economic cost, important steps have been taken over the last many decades to reduce and control emissions of heavy metals in order to protect the environment and public health. Monitoring has confirmed the success of these policies with progressive declines of heavy metals in for example air, sewage sludge and environmental samples. For zinc, such improvements may nevertheless be counter-acted by its widely usage as a feed additive and veterinary medicinal product to piglets in the post-weaning period resulting in reduced occurrence of diarrhea and improvement of daily weight gain. This review therefore focuses on two major concerns associated with veterinary use of zinc, namely the quantifiable risks to the environment and promotion of (multi) resistant bacteria like LA-MRSA in pig farms. Denmark is used as an informed and realistic worst-case scenario, representing the largest pig production per capita in Europe. It is furthermore, one of the countries where most recent information can be found regarding soil monitoring data and zinc consumption within the pig production. An average increase in soil concentration by >45% was recently reported within the period 1998-2014. In order to predict future risk, this review presents new and simplified model predictions using current soil concentrations, annual load rates and predicted accumulation rates. In conclusion, it is estimated that within 25 years, continued agricultural practice of current zinc loads may result in a situation where almost all soils receiving manure from intensive piglet production may be at risk, but also other pig production types may result in scenarios with predicted risk to soil dwelling species, especially in sandy soils. Besides the quantifiable risks to soil ecosystems, high levels of zinc furthermore co-select for the persistence of LA-MRSA CC398 and other resistant bacteria on pig farms.