Humic substances increase survival of freshwater shrimp Caridina sp. D to acid mine drainage
journal contributionposted on 06.12.2017, 00:00 by Aleicia Holland, Leo Duivenvoorden, Susan Kinnear
Humic substances (HS) are known to decrease the toxicity of heavy metals to aquatic organisms, and it has been suggested that they can provide buffering protection in low pH conditions. Despite this, little is known about the ability for HS to increase survivorship to acid mine drainage (AMD). In this study, the ability of HS to increase survivorship of the freshwater shrimp (Caridina sp. D sensu Page, Choy & Hughes, 2005) to acid mine drainage was investigated, using test waters collected from the Mount Morgan open pit in Central Queensland and the addition of Aldrich humic acid (AHA). The AMD water from Mount Morgan open pit is highly acidic (pH 2.67) as well as being contaminated with heavy metals (1780 mg/L Al; 101 mg/L Cu; 173 mg/L Mn; 51.8 mg/L Zn and 51.8 mg/L Fe). Freshwater shrimp were exposed to dilutions in the range of 0.5 - 5 % AMD water, with and without the addition of 10 or 20 mg/L AHA treatments. In the absence of HS, all shrimp died in the 2.5% AMD treatment. By contrast, addition of HS increased survivorship in the 2.5% AMD by up to 66%, as well as significantly decreasing the concentration of dissolved Cu, Co, Cd and Zn. The decreased toxicity of AMD in the presence of HS is likely to be due to the complexation and the precipitation of heavy metals with the HS; it is also possible that HS caused changes to the physiological condition of the shrimp, thus increasing their survival. These results are valuable in contributing to an improved understanding of potential role of HS in ameliorating the toxicity of AMD environments.