The effect of natural dissolved organic carbon on the acute toxicity of copper to larval freshwater mussels (glochidia)

Abstract

The present study examined the effect of dissolved organic carbon (DOC), both added and inherent, on Cu toxicity in glochidia, the larvae of freshwater mussels. Using incremental additions of natural DOC concentrate and reconstituted water, a series of acute copper toxicity tests were conducted. An increase in DOC from 0.7 to 4.4 mg C/L resulted in a fourfold increase (36 150 mg Cu/L) in the 24 h median effective concentration (EC50) and a significant linear relationship (r 2 0.98, p 0.0008) between the DOC concentration and the Cu EC50 of Lampsilis siliquoidea glochidia. The ameliorating effect of added DOC on Cu toxicity was confirmed using a second mussel species, the endangered (in Canada) Lampsilis fasciola. The effect of inherent (i.e., not added) DOC on Cu toxicity was also assessed in eight natural waters (DOC 5 15 mg C/L). These experiments revealed a significant relationship between the EC50 and the concentration of inherent DOC (r 2 0.79, p 0.0031) with EC50s ranging from 27 to 111 mg Cu/L. These laboratory tests have demonstrated that DOC provides glochidia with significant protection from acute Cu toxicity. The potential risk that Cu poses to mussel populations was assessed by comparing Cu and DOC concentrations from significant mussel habitats in Ontario to the EC50s. Although overall mean Cu concentration in the mussel's habitat was well below the acutely toxic level given the concentration of DOC, episodic Cu releases in low DOC waters may be a concern for the recovery of endangered freshwater mussels. The results are examined in the context of current Cu water quality regulations including the U.S. Environmental Protection Agency's (U.S. EPA) biotic ligand model.

Freshwater Mussel Population Status and Habitat Quality in the Clinch River, Virginia and Tennessee, USA: A Featured Collection

“…Cherry et al (1991) summarized these events, highlighting that Cu was detrimental to mussel growth and physiological activity at water concentrations in the 15-20 lg/l range, with acutely toxic effects noted at 19.4 lg/l. Additional research reported Cu-acute toxicity levels (median effective concentrations, EC50s) as low as 17-36 lg/l for native freshwater mussels (Jacobson et al, 1993;Gillis et al, 2010).…”

Humic Substances Increase Survival of Freshwater Shrimp Caridina sp. D to Acid Mine Drainage

“…Shrimp survival in AMD water substantially increased in the presence of both 10 and 20 mg/L AHA. Decreases in toxicity of heavy metals to invertebrates and fish have been shown to occur in the presence of HS (Dobranskyte et al 2006;Gillis et al 2010;Schwartz et al 2004). The decrease in toxicity of heavy metals in the presence of dissolved organic carbon (DOC), such as HS, has been (2005) Dashes not tested a Dissolved metals b Total metals recorded (Chapman and Simpson [2005]) suggested to be due to the complexation of metals by DOC.…”

“…It has been suggested that the presence of high amounts of HS in naturally acidic waterways buffers the organisms present against the detrimental effects of low pH (Collier et al 1990; Dangles et al 2004). HS have also been shown to decrease the toxicity of heavy metals to aquatic organisms across a number of different trophic levels (Gillis et al 2010;Kim et al 1999;Schwartz et al 2004). Despite this, the ability of HS to increase survival to anthropogenically acidified waters, such as those affected by AMD, is unknown.…”

Transgenerational Effects of Copper on a Freshwater Gastropod, Planorbella pilsbryi

“…Dissolved organic carbon (DOC) and other sources of organic material can bind to aqueous Cu, reduce its bioavailability, and ameliorate toxicity (Allen et al 1980;Erickson et al 1996;Schwartz et al 2004). Increasing levels of DOC in laboratory exposures have been shown to reduce Cu toxicity to molluscs (Gillis et al 2008(Gillis et al , 2010Wang et al 2009). In the Parental Exposure, all replicates were fed identical quantities of spinach and contained the same number of snails, in an effort to limit variation in organic matter and thus variation in bioavailable Cu.…”

“…As this is not an exhaustive evaluation of Cu in the environment, it is important to note other modifying factors that can affect bioavailability and thus the toxicity of Cu in natural aquatic systems. For example, Gillis et al (2010) reported that Cu EC50s were up to three-fold higher when freshwater mussel glochidia were exposed in Cuaugmented natural water compared to Cu-augmented reconstituted laboratory water. While we cannot comment on how frequently Cu concentrations in the environment may exceed the multigenerational effect concentrations reported here without accounting for possible modifying factors, our study demonstrates that even one pulse event at potentially environmentally relevant concentrations can cause significant detriment to the next generation.…”