Insecticides

Pesticides applied in agriculture can affect the structure and function of nontarget populations at lower doses and for longer timespans than predicted by the current risk assessment frameworks. We identified a mechanism for this observation. The populations of an aquatic invertebrate (Culex pipiens) exposed over several generations to repeated pulses of low concentrations of the neonicotinoid insecticide (thiacloprid) continuously declined and did not recover in the presence of a less sensitive competing species (Daphnia magna). By contrast, in the absence of a competitor, insecticide effects on the more sensitive species were only observed at concentrations 1 order of magnitude higher, and the species recovered more rapidly after a contamination event. The underlying processes are experimentally identified and reconstructed using a simulation model. We conclude that repeated toxicant pulse of populations that are challenged with interspecific competition may result in a multigenerational culmination of low-dose effects.

The method used to approve pesticides in the EU needs to be revised. This was confirmed by a recent study by the Institute for Environmental Sciences Landau. According to the study, the level of fungicides measured in surface waters is often much higher than the level predicted by the current calculation model used in the approval process. Last year a study by the Institute on insecticides had a similarly alarming conclusion.

Unless regulators take action, one of gifts in the lyrics to “Twelve Days of Christmas,” the turtle dove, may become extinct. The dove has experienced major population decline in England over the past 20 years, due in significant part to the destruction of turtle dove habitat and food sources from increasing herbicide use in English agriculture. Other species, such as Monarch butterflies and other pollinators around the world, are also experiencing similar loses of habitat and food sources through an increase in herbicide use. These increasing rates of population decline in wild species underscore the problem that chemical-intensive agriculture plays in the degradation of natural habitats.

Rising levels of cancers and fertility problems have attracted scientists’ attention to endocrine disrupting chemicals, with some calling for strict regulation of the substances, in line with the precautionary principle. Others meanwhile, stress the worthiness of those chemicals in everyday products such as plastics and warn that the foundations of science risk being turned upside down if precautionary measures are taken. Endocrine disruptors are suspected of triggering diseases such as cancer or diabetes and contributing to people becoming overweight or infertile. The controversy has gone beyond the traditional confrontation between the chemicals industry and environmental and health activists. Among scientists, too, opinions vary on whether a link exists between these chemicals and diseases. But all parties agree on one point – that the protection of consumers and the environment must be ensured. Henk Tennekes comments that a new risk assessment is needed to evaluate the effects that chemicals have on humans and the environment and that endocrine disruptors may be a case in point.

Neonicotinoid insecticides like thiacloprid enter agricultural surface waters, where they may affect predator-prey interactions, which are of central importance for ecosystems as well as the functions these systems provide. The effects of field relevant thiacloprid concentrations on the leaf consumption of Gammarus fossarum (Amphipoda) were assessed over 96 h (n = 13-17) in conjunction with its predation on Baetis rhodani (Ephemeroptera) nymphs. The predation by Gammarus increased significantly at 0.50-1.00 ug/L. Simultaneously, its leaf consumption decreased with increasing thiacloprid concentration. As a consequence of the increased predation at 1.00 ug/L, gammarids’ dry weight rose significantly by 15% compared to the control. At 4.00 ug/L, the reduced leaf consumption was not compensated by an increase in predation causing a significantly reduced dry weight of Gammarus (~20%). These results may finally suggest that thiacloprid adversely affects trophic interactions, potentially translating into alterations in ecosystem functions, like leaf litter breakdown and aquatic terrestrial subsidies.