The effects of low hardness and pH on copper toxicity to Daphnia magna

Abstract

The majority of metal toxicity data available for freshwater organisms have been generated in laboratory water at pH > 6.5 and hardness > 50 mg/L as CaCO3. Extrapolation of these results to soft surface waters (i.e., hardness < or = 40 mg/L as CaCO3), similar to predominant conditions in the southeastern United States, may prove challenging. For example, South Carolina has surface waters that average 20 mg/L as CaCO3, and exist at extremes of 1 and 600 mg/L as CaCO3. This research characterized the acute toxicity of Cu to Daphnia magna in waters with low hardness and low pH. The 48-h total Cu median lethal concentrations were related to water hardness over a hardness range of 8 to 51 mg/L as CaCO3. Although toxicological differences existed between water hardness of 7 and 20 mg/L as CaCO3 (p = 0.0001), differences in pH (range 5.5-8.5) did not influence acute Cu toxicity. Results of these laboratory studies will provide the data needed to more accurately predict organism response to Cu in waters with low pH and low hardness.

Combined effects of pH, hardness and dissolved organic carbon on acute metal toxicity to Daphnia magna

“…This well agrees with the works of other researchers [5,6,19]. As pH decreases, the toxicity of Cu(II) increases due to increase of toxic free copper ions (Cu 2+ ) [19]. For Cr(VI), toxicity to D. magna was decreased at both pH 6 and 8 compared with that of pH 7.…”

“…This reduction of Cu(II) toxicity is caused by increase of complex formation between Cu(II) and DOC [5]. In general, copper associated with organic matter is considered to be non-bioavailable or non-toxic to aquatic organisms [19]. Contrary to Cu(II) toxicity, Cr(VI) toxicity was not influenced by DOC concentration.…”

Effect of hardness on acute toxicity of metal mixtures using Daphnia magna: Prediction of acid mine drainage toxicity

“…A recent study has demonstrated an inverse relationship between copper toxicity of D. magna and hardness. Low concentrations of hardness, ranging from 7 to 50 mg/L as CaCO 3 , significantly affected the copper toxicity [21]. Therefore, it is clear that hardness is a major factor affecting metal toxicity and should be considered in determining reference LC 50 values when the toxicities of metal mixtures on aquatic species are evaluated.…”

Evaluation Of The Biotic Ligand Model For Predicting Metal Bioavailability and Toxicity In SRS Effluents And Surface Waters

“…With the exception of research published by Long et al (2004) and Van Genderen et al (2005), there has been very little BLM work done in low hardness waters. Long et al (2004) investigated the effects of low hardness and pH on copper toxicity to Daphnia magna.…”

“…With the exception of research published by Long et al (2004) and Van Genderen et al (2005), there has been very little BLM work done in low hardness waters. Long et al (2004) investigated the effects of low hardness and pH on copper toxicity to Daphnia magna. They prepared one set of synthetic water that had the same pH and varied the hardness (7.9 to 50 .7 mg/l) and a second set of synthetic waters that either had a hardness of 7.1 or 20.6 mg/l.…”