A comparison of the copper sensitivity of two economically important saltwater mussel species and a review of previously reported copper toxicity data for mussels: Important implications for determining future ambient copper saltwater criteria in the USA

Abstract

Saltwater bivalves of the genus Mytilus are among the most copper sensitive taxa listed in both the current and recently proposed U.S. EPA ambient saltwater copper criteria documents. The copper saltwater quality criteria are somewhat unique in that the criteria were set specifically to protect Mytilus. However, there is considerable uncertainty in the reported taxonomy of Mytilus species in the criteria database and it has recently been demonstrated the copper toxicity to M. galloprovincialis is dependent on the organic matter content of the test water. A review of the toxicity and biogeography literature was conducted to rationalize the existing criteria database. Elimination of some data is suggested due to the uncertainty of test organism genotype. Moreover, due to the lack of reported dissolved organic matter content of the test waters in tests included in the criteria database, it is impossible to determine if the difference in species mean acute values reported in the criteria documents for Mytilus was due to differences in water chemistry or differences in species sensitivity. Experiments were designed and conducted with M. galloprovincialis and M. edulis (genetically confirmed) to determine if copper toxicity is a function of organic matter content for these two species and if there is a significant difference in species copper sensitivity. Results showed that copper toxicity is a function of organic matter concentration for both species and copper sensitivity of each species was statistically similar. Results support the normalization of the saltwater copper criteria database with respect to dissolved organic matter when developing ambient saltwater copper criteria. The USEPA toxicity database would benefit from future testing of M. trossulus and M. californianus.

A comparison of the copper sensitivity of six invertebrate species in ambient salt water of varying dissolved organic matter concentrations

“…Specimens from this culture have previously been genetically identified to confirm their taxonomy [16].…”

The effect of natural organic ligands on trace metal speciation in San Francisco Bay: Implications for water quality criteria

“…Also, most of Arnold et al's prior work (e.g. Arnold et al, 2009 and documenting a DOC-dependent BLM bias on Cu toxicity to Mytilus sp. was performed with samples from San Francisco Bay.…”

“…As an example, in a study of Cu toxicity to Mytilus sp., Arnold et al (2005) have documented a DOC-dependent systematic bias between observed and BLM-predicted toxicity for estuarine and coastal waters, and they conclude that "the difference is likely due to errors in the BLM treatment of DOC". Since the BLM is essentially a variation on speciation calculation, this implies errors in the fundamental calculation that determines how much, and how strongly metals bind to DOC (Arnold et al, 2009 andNiyogi and Wood;and references therein).…”

“…Mytilus sp. is a commercially important organism (Arnold et al, 2009) that is one of the most sensitive marine species to Cu (Grosell et al, 2007), and Cu is a marine contaminant of increasing prevalence and regulation (State of California, 2010). Using Cu as test case here is further useful since Cu was the metal that was used in initial development of the BLM (U.S. EPA, 2007;2003a and2003b), and hence biotic ligand parameters for Cu have been developed and are available (particulars are given below).…”

“…One approach uses an analytical expression, with fitted parameters from actual toxicity observations, to empirically correct for the bias (Arnold et al, 2009 and. This approach is entirely empirical and makes no assumptions regarding the underlying causative factors.…”