Mammalian steroid hormones can reduce abundance and affect the sex ratio in a soil nematode community

The effect of mammalian steroid hormones (estradiol, estrone, progesterone, and testosterone) in environmentally relevant concentrations on a soil free-living nematode community was examined. Steroids were applied in 2.5 L water on 0.25 m 2 plots in triplicate, and comparison was made with plots receiving water alone. Soil samples were taken from the 0 to 5, 5 to 10, and 10 to 20-cm soil layers. The soil free-living nematode populations were examined at zero time, 12 h, 72 h, 96 h, 120 h, and 25 d post-treatment. Testosterone, progesterone, and estrone were persistent in the soil while the estradiol rapidly dissipated. The total number of nematodes was decreased by the presence of testosterone, progesterone, or estrone but not estradiol. Testosterone, progesterone, and estrone increased the number of males in relationship to females (60:40) compared to the control and estradiol-treated plots (50:50). The presence of steroids had no consistent effect on the distribution of bacteria-feeders, plant-feeders, and omnivore-predators. We conclude that the addition of steroid hormones in the soil can reduce abundance and change the sex ratio in a free-living nematode community. This would be the first demonstration of an effect of an endocrine-active agent excreted by mammals on a free-moving terrestrial organism.