Interaction effects of multi-metal solutions (As, Cr, Cu, Ni, Pb and Zn) on life history traits in the rotifer Plationus patulus.

While many studies have determined toxicity of single heavy metals, few have addressed the combined effects of multiple elements at different concentrations. In order to estimate how metal mixtures affect population dynamics of freshwater rotifers, we exposed Plationus patulus to environmentally relevant concentrations and combinations of arsenic and five heavy metals (Cr, Cu, Ni, Pb and Zn) for 8 days. The life-history parameters, intrinsic rate of increase (r), relative cumulative reproduction (RCR), mortality ratio, mictic ratio, fertilization ratio, and number of deformed offspring were used as endpoints. Exposures were repeated 4 times and considered as blocks in the experimental design. Differences between treatments were evaluated through ANOVA and LSD mean analysis. The combined presence of As, Cu, Ni, Pb, and Zn in different concentrations produced a variety of changes in the population dynamics of P. patulus. However, only Cr produced a significant element*environment interaction. The presence of Cr leads to significant decreases in the intrinsic rate of increase and increased mortality ratio in multi-metal environments. The population growth (as r) decreased from 0.25 to -0.16 due to Cr (10 microg/L) interaction with the remaining elements, and values 0.16-0.12 were observed in treatments containing high levels (50 microg/L) of Cr. Mortality ratio increased from 0.066 to 0.822 due to Cr (10 and 50 microg/L) interactions with the remaining elements at high concentrations. Responses of this basal consumer to metal mixtures will provide insights into how aquatic food webs and their constituent organisms can be altered by anthropogenic inputs like heavy metal contamination.