Failure of Hydra populations to develop tolerance, indicates absence of toxicity from a mining whole-effluent

摘要

The green hydra, Hydra viridissima, exists in water bodies on the Project Area of the Ranger Uranium Mine (RUM) in northern Australia, which contain concentrations of magnesium (Mg), higher than those reported to cause toxicity from the Environmental Research Institute of the Supervising Scientist ( eriss) laboratory toxicity tests. McCULLOUGH (2006) reported a lowest-observedeffectconcentration (LOEC) for H. viridissima of 4.6 mg L~(-1) Mg, (present as MgSO_4), which represented a population growth rate decrease of approximately 30% relative to the control response. The same study found that toxicity was due to Mg and not S0_4. However, CORBETT (1996) reported the presence of H. viridissima in water bodies on the RUM Project Area containing Mg concentrations above this LOEC, and theoretically high enough to severely impact population growth (i.e., 10-20 mg L~(-1)). The disparity between the eriss laboratory and field results raised the question of how H. viridissima could exist in these contaminated environments. Interactions between chemical compounds in complex mixtures can result in antagonistic effects that reduce toxicity (WARNE 2003). In addition, however, adaptation of aquatic organisms exposed to elevated contaminant concentrations can occur (DIXON & SPRAGUE 1981, GALE et al. 2003). The presence of H. viridissima in the contaminated water bodies could potentially be explained by one or both of these factors. This study sought to determine whether H. viridissima from a water body containing elevated Mg exhibited increased tolerance to Mg by comparing their responses to those of H. viridissima from eriss laboratory stock. We exposed cultures from both populations to a series of concentrations of (1) contaminated billabong water from the RUM Project Area, and (2) Mg-spiked natural creek water.