Effects of a long term exposure of bisphenol-A on macrophyte and invertebrate populations and communities in lotic mesocosms
Résumé
Bisphenol-A is manufactured for the plastics industry as an intermediate in the production of polycarbonate and epoxy resins. Around 3 million tons of this substance is produced each year worldwide. There is evidence from numerous in vitro and in vivo studies that BPA exhibits an estrogen-mimetic action at concentrations as low as 2 µg L-1. As high levels of BPA have been reported in the aquatic environment, potential effects on aquatic ecosystems are suspected. Nevertheless, to current knowledge, few studies have been performed to assess the long term effects of BPA at the population and community levels. A lotic mesocosm study was thus carried out, in twelve 20 meter long channels, under continuous, environmentally realistic concentrations of bisphenol A (1, 10 and 100 µg L-1 in trireplicats). The mesocosms were set up with artificial sediments, macrophytes, periphyton, benthic and pelagic invertebrates, decomposers and one fish species (Gasterosteus aculeatus). Care was taken to ensure equal stocking densities in each mesocosm. Treatment began on the 15th of April 2012 and followed on for 6 months until the 29th of September 2012. Periphyton biomass, macrophyte biovolume, zooplankton and invertebrate abundance and diversity and fish population dynamics were the measured biological endpoints. The biovolume of watercress, Nasturtium officinale, was significantly and negatively affected at the highest tested concentration. In order to account for the observed effects, concentrations of BPA in plant tissue and roots are currently being measured.Community structure of macroinvertebrate was also affected at 100 µg L-1 with Oligocheata and Planariidae being the most sensitive taxa. Gasteropods and Chironomes on the contrary increased in abundance. More specifically, fecundity of Radix peregra was significantly increased resulting in a modification of the population structure. The extent to which the alterations in population and community structure of lower trophic levels affected the responses of higher trophic levels such as fish is discussed. The authors highlight the importance of indirect effects which results mainly from competition and predation in structuring the overall toxic response.