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Endpoint:
additional ecotoxicological information
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Study period:
2012
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
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1. HYPOTHESIS FOR THE ANALOGUE APPROACH
[Describe why the read-across can be performed (e.g. common functional group(s), common precursor(s)/breakdown product(s) or common mechanism(s) of action]

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
[Provide here, if relevant, additional information to that included in the Test material section of the source and target records]

3. ANALOGUE APPROACH JUSTIFICATION
[Summarise here based on available experimental data how these results verify that the read-across is justified]

4. DATA MATRIX
Cross-reference
Reason / purpose:
read-across: supporting information

Data source

Reference
Reference Type:
publication
Title:
Overview of Copper Toxicity to Aquatic Life
Author:
Okocha, R.O., Adedeji, O.B.
Year:
2012
Bibliographic source:
Report and Opinion 2012; 4:(8)

Materials and methods

Test guideline
Qualifier:
no guideline required
Version / remarks:
This is a review of published studies on copper toxicity to aquatic life
GLP compliance:
no
Remarks:
not applicable. This is a review.

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
not specified

Results and discussion

Any other information on results incl. tables

Environmental factors

A number of factors will determine the toxicity of copper in water: a) the amount of free copper (Cu2+) in the water; b) the sensitivity of the fish or invertebrate species exposed; c) the age of the fish; d) the acclimation time to target concentration; e) the presence of substrates, especially those made of calcium or magnesium carbonate (including dolomite, oysters shell, and coral), that may remove copper from the water by adsorption; f) the presence of dissolved substances that may bind with copper and reduce its activity, including carbonates; g) the presence of "live foods" that may absorb and bioaccumulate (biologically concentrate) copper in their bodies; and h) the tank water pH (Cardeilhac and Whitaker 1988). Because copper levels can vary over time--for instance, they may suddenly increase with a drop in pH--copper concentration should be measured at least twice a day and adjusted accordingly.

Effects on Aquatic Organisms

Copper is an essential compound for aquatic organisms in small quantities. However, copper becomes toxic when biological requirements are exceeded. The effects of copper on aquatic organisms can be directly or indirectly lethal. Different species, and even organisms within the same species, can exhibit different sensitivities to elevated copper levels in the water column. Organisms have different mechanisms by which they cope with and process copper. Some organism bioaccumulate and store copper, whereas others actively regulate its levels. In general, copper is actively regulated in fish, decapod crustaceans, and algae and stored in bivalves, barnacles, and aquatic insects (Brix and Deforest 2000). Therefore, to properly evaluate the copper-related effects on aquatic life, one must understand the factors that affect the biological fate of copper and the mechanisms by which it acts to produce its toxicity.

Copper undergoes complex speciation in natural waters; some species are bioavailable (free Cu2+ and Cu+ ions), while others are not. Only bioavailable forms of copper are considered to be toxic to exposed organisms. The reference to “copper” and “free copper” in the following discussion refers to its bioavailable form. The bioavailability, biodistribution to various parts of the organism, and bioaccumulation of copper are dramatically influenced by water chemistry. Therefore, water pH, hardness, organic content, and salinity play important roles in copper-induced toxicity.

The majority of studies in which the toxicity of copper has been addressed were performed on freshwater species. Copper is generally more toxic to organisms in freshwater than in saltwater. One of the reasons for this difference is that freshwater lacks cations, which compete with Cu2+ at the biological action sites, thus reducing copper toxicity (Brooks et al. 2007). Consequently, pH and water hardness play more important roles in freshwater than in saltwater environments. Increased pH accentuates copper toxicity because of the reduced competition between copper and hydrogen ions at the cell surface (Wilde et al. 2006). Cations that are involved in water hardness (i.e., Ca2+ and Mg2+) also compete with Cu2+ for biological binding sites (Boulanger and Nikolaidis 2003). Therefore, Cu2+ is less bioavailable in hard water than in soft water.

Although water pH and hardness protect organisms against Cu toxicity to some degree, the DOC content is among the most important factors in reducing copper toxicity to both fresh- and salt-water species. DOC forms organic complexes with copper and thereby reduces copper’s bioavailability. According to McIntyre et al. (2008), water hardness and pH are unlikely to protect fish from copper-induced sensory neurotoxicity. However, water that contains high DOC concentrations does diminish the toxic effects of copper on the peripheral olfactory nervous system in Coho salmon (Oncorhynchus kisutch) (McIntyre et al. 2008). High DOC levels also significantly decrease acute copper toxicity to the freshwater flea, Daphnia magna, and the estuarine copepod, Eurytemora affinis (Hall et al. 2008; Kramer et al. 2004). Study results show that the water salinity gradient can also significantly affect the biological fate of copper.Water salinity influences the biodistribution and bioaccumulation of copper and can affect its toxicity as well (Amiard-Triquet et al. 1991; Blanchard and Grosell 2005; Grosell et al. 2007; Hall et al. 2008). The biodistribution of copper throughout the gill, intestine, and liver of the common killifish, Fundulus heteroclitus, is salinity dependent (Blanchard and Grosell 2005).

According to these authors, the gill and the liver are important target organs for copper accumulation at low salinities, whereas the intestine is a target organ at high salinities. In addition, the liver is a major organ involved in copper homeostasis and accumulates the highest amounts of copper. For this reason, the liver may be a potential target organ during chronic copper exposure. Water salinity influences the biodistribution and the toxicity of copper. Grosell et al. (2007) found killifishes to be most tolerant to copper exposure at intermediate salinities, and the acute toxicity was significantly higher in the lowest and highest salinity water. Increased fish sensitivity at both salinity extremes can be attributed to two factors: changes in copper speciation and changes in fish physiology in changing aquatic environments.

In general, water salinity may be more important to species that actively regulate internal osmotic pressure. The majority of invertebrates, however, are osmoconformers. Hence, to them the salinity gradient may be less important. Although in bivalves, the biological fate of copper was salinity dependent, in copepods (Eurytemora affinis) the toxicity of copper correlated better to DOC content than water salinity (Hall et al. 2008). In oysters, copper accumulation was inversely related to salinity (Amiard-Triquet et al. 1991). Some species can adapt to tolerate higher pollutant levels. Damiens et al. (2006) described adult oysters that lived in polluted water, wherein their larvae become less sensitive to pollution over time. Phytoplankton species have different sensitivities to copper toxicity: cyanobacteria appear to be most sensitive, coccolithophores and dinoflagellates show intermediate sensitivity, and diatoms are resistant to copper (Brand et al. 1986; Beck et al. 2002).

Copper is stored and transported inside an organism as inorganic and organic complexes. In killifishes, copper bioaccumulates in target organs primarily as copper carbonate (CuCO3) and, to a lower extent, as copper hydroxide (CuOH+ and Cu(OH)2) (Blanchard and Grosell 2005). Bivalves accumulate considerable amounts of copper that is associated with a cytosolic protein called metallothionein (Claisse and Alzieu 1993; Damiens et al. 2006). Although copper bioaccumulates and biodistributes to different organs, it is an internally regulated essential micronutrient. Therefore, according to Brix and Deforest (2000), there is an inverse relationship between metal concentrations in the water and in the organism. Hence, the bioconcentration factor (BCF) is not a suitable concept to describe the bioconcentration of copper.

Toxicity data for aquatic species for copper oxide, selected from the U.S. EPA ECOTOX database, are summarized in Table 1 (U.S. EPA 2009a; please see below). The table is divided into sections for freshwater and saltwater organisms. Data are presented for fish, invertebrates, and plants. The toxicity endpoints are also presented in the table, as is the chemical concentration that was lethal (LC50) or produced an effect (EC50). There is a large range in copper toxicity values for different freshwater algae.

Applicant's summary and conclusion

Conclusions:
The copper toxicity to aquatic species vary significantly depending on pH, hardness, organic content and salinity.
Executive summary:

A number of factors determine the toxicity of copper in water: a) the amount of free copper (Cu2+); b) the sensitivity of the fish or invertebrate species exposed; c) the age of the aquatic species; d) the acclimation time to target concentration; e) the presence of substrates, especially those made of calcium or magnesium carbonate (including dolomite, oysters shell, and coral), that may remove copper from the water by adsorption; f) the presence of dissolved substances that may bind with copper and reduce its activity, including carbonates; g) the presence of "live foods" that may absorb and bioaccumulate (biologically concentrate) copper in their bodies; and h) the tank water pH.