Interactions of selenium with other pollutants on aquatic and terrestrial food webs

Background/Question/Methods Although most contaminated sites contain multiple pollutants, relatively few studies examine both the independent and joint effects of multiple contaminants. For example, in the Pacific Rim countries, selenium and mercury co-occur over large areas. Similarly, due to industrial and military activity, hexavalent chromium and perchlorate contamination overlap in much of the southwestern USA. Surprisingly little is known of the effects of contaminants on insects, which are critical to ecosystem function. A series of laboratory experiments on terrestrial and aquatic insects were conducted to address the following questions: 1) do different metals and metal species have similar relative toxicities across guilds, 2) how does mercury affect the toxicity of selenium and, 3) is there an interaction between metals such as hexavalent chromium and other pollutants such as perchlorate? Results/Conclusions The answers to the key questions were definitive. Some guilds of insects were relatively tolerant of metals, particularly detritivores. At least some predators and parasites appear to have evolved mechanisms to avoid or eliminate metal pollution acquired from their prey. Joint effects were mixed, but in systems with mercury and selenium or hexavalent chromium and perchlorate, the combinations of chemicals were substantially more toxic than would be expected from the independent effects. Selenomethionine is the most critical form of selenium found in insects when only selenium is present, but when mercury co-occurs with selenium, seleno-cysteine/cysteine predominates. The implications for insect populations will be discussed, along with suggestions for future research.