The impact of hormones on below ground interactions

A key requirement for a circular bio-economy is that rest products, e.g. faeces, urine, sewage sludge, are returned to soil for replenishing nutrients for crops. However, a major concern is that these by-products contain hormones, both natural and from medicinal treatments and reproductive manipulations (e.g. estradiol), which might affect soil biodiversity including the most abundant animals: nematodes. Mammalian hormones from surface water are known to negatively impact above-ground invertebrates. We here aimed to study impact of hormones from by-product-fertilizers on the below-ground soil ecosystem, using nematodes as a model. For this, a system approach was chosen, analyzing both fate and effects of hormones in soils. As a starting point our results show that bacterivorous nematode abundance is directly affected by hormones in-vitro, confirming nematode utility as ecotoxicological indicators. Subsequently, in an end-point context in the food system, in hormone contaminated soil with growing crops, results show that bacterivorous nematode abundance was halved in a three week time span by application of hormones, indicating serious impact on the soil food web. We quantified hormones in soil and crops, which appeared largely metabolized ( 80%). We found that crops take up and translocate hormones, including higher estrogenic active metabolites, to their edible parts, indicating possible food safety risks. We show that hormones impact soil biodiversity and even end up in plants, which could lead to a circle ending in humans. This calls for a close watch on the ecological impact in soil of pharmaceutically active substances, and hazards originating from circular agricultural practices.