Modelling ecotoxicity of polybrominated diphenyl ethers in aquatic ecosystems

Abstract

Polybrominated diphenyl ethers (PBDEs) are commercially-produced substances that are used as flame retardants in a wide variety of consumer products. They are among chemicals of emerging environmental concern and are found to be ubiquitous in the environment--they were detected in sediments, water, fish, and wildlife and in human adipose tissues. Environmental concentrations are lower than those of other persistent organic pollutants (POPs). However, present data show that while levels of POPs such as PCBs and DDT are decreasing, PBDE levels are definitely on the rise. The two most prevalent PBDEs in the environment are BDE47 and BDE99. This research studied the toxicity of PBDEs using Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum), Daphnia magna, and Hyalella azteca in laboratory bioassays, by exposing each species to 5 different concentrations (0, 12.5, 25, 50, 100, and 200 [micro]g/l) of BDE47 and BDE99 congeners. PBDEs showed toxicity to D. magna and P. subcapitata and growth was inhibited at the lowest concentration tested, (12.5 [micro]g/l). Neither of the two congeners had measurable effects (in particular, mortality) on H. azteca at the concentrations tested (up to 200 [micro]g/l). A model was developed in order to understand effects of PBDEs on grazing (or predator-prey) relationships using P. subcapitata as a prey species and D. magna as a grazer or predator species. In general, PBDEs have demonstrated the ability to have significant impact on population dynamics of species in a grazing relationship, even at concentrations that caused minimal effects in growth parameters of isolated species. While single species bioassays showed a decrease in biomass of both species with increasing concentrations of PBDEs, our model predicts an increase in algal population, and a disproportionate and significant decline in Daphnia. The research suggest that PBDEs in the natural environment therefore, will not only cause toxic effects on individual sensitive species but also on populations of other organisms with which they interact.