Responses of three benthic organisms (Hyallela azteca, Limnodrillus hoffmeisteri and Stagnicola attenuata) to natural sediment spiked with zinc when exposed in single or multi-species test systems

In order to determine the influence of the presence of one or more species in a system on Zn toxic response, acute (LC50 at 72 h) and sublethal toxicity (Zn uptake kinetics, and quantification of total protein content and lipid peroxidation levels) were evaluated in three benthic organisms (Hyallela azteca, Limnodrillus hoffmeisteri and Stagnicola attenuata). They were exposed either singly or together (single or multi-species test systems) to Zn-spiked sediment from Ignacio Ramirez Reservoir. Both assays showed that Zn-spiked sediments from Ignacio Ramirez Reservoir were toxic to S. attenuata, L. hoffmeisteri and H. azteca, and that toxic response was modified according to the number of species in the system. These differences may be due to multiple factors: such as benthic bioturbation which modifies physical and chemical characteristics of sediments and affects the fate and partitioning of sediment-bond contaminants, such as spiked Zn or other pollutants in sediments from Ignacio Ramirez Reservoir. In addition, the presence of more than one species in the system may lead to microenvironmental changes (pH, temperature, and organic matter and metabolic waste content), which can also contribute to toxic response differences. Also, particular characteristics of each of the species involved in the study became evident. The snail and amphipod are facultative benthic organisms, while the worm is obligate. Such way of life differences may have modified the bioavailability of contaminants, determining their toxicity.