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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

General summary of the information on environmental fate and pathways

Copper is a natural element and transition metal with more than one oxidation state. Copper in its metallic form (Cu°) is not available. Copper needs to be transformed to its ionic forms to become available for uptake by living organisms

Stability and Biodegradation

The classic standard testing protocols on hydrolysis, photo-transformation, are not applicable to copper and copper compounds.

This was recognized in the Guidance to Regulation (EC) No 1272/2008 Classification, Labelling and Packaging of substances and mixtures (metal annex): ‘Environmental transformation of one species of a metal to another species of the same does not constitute degradation as applied to organic compounds and may increase or decrease the availability and bioavailability of the toxic species. However as a result of naturally occurring geochemical processes metal ions can partition from the water column. Data on water column residence time, the processes involved at the water – sediment interface (i.e. deposition and re-mobilisation) are fairly extensive, but have not been integrated into a meaningful database. Nevertheless, using the principles and assumptions discussed above in Section IV.1, it may be possible to incorporate this approach into classification.’ For a discussion on this please see Section 7.6.

Relevant fate aspects for copper in the environment have been included in the section ‘additionalinformation on fate and pathways’ and are summarized below.

As outlined in theguidance (2009 and 2012), the understanding of the transformation of copper into more or less bioavailable species is relevant to the environmental hazard assessments and this is described below.

- Transformation of Cu-ions released in the environment - Copper speciation

Once released to the environment, copper ions have more than one oxidation state and copper is thus characterized as transition metal. The principal ionic forms are cuprous (Cu(I), Cu+) and cupric (Cu(II), Cu2+). The trivalent form (Cu(III), Cu3+) occurs but is relatively unimportant in physical and biological systems. Cu+is unstable in aqueous media and soluble Cu1+compounds readily transforms into soluble Cu2+ions, compounds and/or insoluble Cu2+ions, compounds (e.g. copper sulphides) that precipitate. This transformation of Cu+to Cu2+is a result of a redox reaction initiated through atmospheric water vapour as well as in aqueous solution. However, monovalent copper cations are only susceptible to such transformation when they are not chemically bound in insoluble compounds or stabilised in complexed forms.

The transformation of Cu(I) to Cu (II) can be described by:

 (1) 2 Cu2O + 2H2O = 4Cu++ 4OH-

and

 (2) 4Cu++ O2+ 4H+= 4Cu2++ 2H2O

 Both sub-reactions are summarised as:

2Cu2O(s) + O2(g) + 4H+= 4Cu2++ 4OH-

Among the copper species released/transformed, Cu (II) is thus the most environmental relevant species. It is further recognised that Cu (II) ions - commonly named free cupric ions- are the most active copper species and that total Cu or Cu(II) concentrations are usually not directly related to ecological effects since exposure of biota may be limited by processes that render Cu unavailable for uptake (ICPS, 1998). Assessing the species of Cu (II) therefore has ecotoxicological relevance. After being released into the environment, the Cu(II) ions typically bind to inorganic and organic ligands contained within water, soil, and sediments. In water Cu(II) binds to dissolved organic matter (e. g. humic or fulvic acids). The Cu(II) ion forms stable complexes with -NH2, -SH, and, to a lesser extent, -OH groups in these organic acids. Cu(II) will also bind with varying affinities to inorganic and organic components in sediments and soils. For example, Cu(II) binds strongly to hydrous manganese and iron oxides in clay and to humic acids, but much less strongly to aluminosilicates in sand. In all environmental compartments (water, sediment, soil), the binding affinities of Cu(II) with inorganic and organic matter is dependent on pH, the oxidation-reduction potential in the local environment, and the presence of competing metal ions and inorganic anions.

Some key papers on copper speciation in freshwater, marine waters, sediments and soils are provided in the section ‘additional information on environmental fate

- Copper attenuation, removal from water column, geochemical cycling- Quantitative assessment

As described above, after the release of Cu(II) in the environment, further transformations occur thereby changing the potential for toxicity, induced by the free cupric ions. The concentrations of ‘active’ cupric ions, that remains available for uptake by biota depends on different processes: precipitation, dissolution, adsorption, desorption, complexation and competition for biological adsorption sites (ligands). These processes are critical for the fate of copper in the environment. This was recognized in the Guidance to Regulation (EC) No 1272/2008 Classification, Labelling and Packaging of substances and mixtures (metal annex):

‘Environmental transformation of one species of a metal to another species of the same does not constitute degradation as applied to organic compounds and may increase or decrease the availability and bioavailability of the toxic species. However as a result of naturally occurring geochemical processes metal ions can partition from the water column. Data on water column residence time, the processes involved at the water – sediment interface (i.e. deposition and re-mobilisation) are fairly extensive, but have not been integrated into a meaningful database. Nevertheless, using the principles and assumptions discussed above in Section IV.1, it may be possible to incorporate this approach into classification. ‘

The use of laboratory mesocosm and/or field tests for evaluating removal of soluble metal species through precipitation/partitioning processes over a range of environmentally relevant conditions are described in theguidance (2009) and for copper, such laboratory/mesocosm and/or field tests have therefore been assessed.

-In the water compartment,removal of soluble copper species through precipitation/partitioning processes over a range of environmentally relevant conditions, was assessed in Raderet al.,2013 and described in the section ‘additional information on environmnetal fate and pathways’.

The assessment relies on modeling simulations, based on the Tableau Input Coupled Kinetics Equilibrium Transport (TICKET) model(Farleyet al.,2008). The numerical engine of the model is a screening level model used to assess the fate and effects of chemicals through simultaneous consideration of chemical partitioning, transport, reactivity, and bioavailability (MacKay TICKET-UWM). The software includes metal-specific binding to inorganic ligands,and POC (using information from metal speciation models such as WHAM) and average-annual cycling of organic matter and sulfide production in the lake. 

The model was applied to a standard lake environment (EUSES characteristics), complemented with a sensitivity analysis on model parameters such as pH. The validity of the model outcome (removal rate) was assessed from mesocosm and field data The main conclusions are formulated as follows:

·   For a standard lake environment consisting of the EUSES model lake parameters and the Kd derived in the copper RA (Log Kd: 4.48), copper removal from the water column satisfies the criterion of rapid removal of 70% dissolved copper removal in 28 days;·   For a standard lake environment consisting of the EUSES model lake parameters but with pH varying between 6 and 8 (Kd estimated form the model), copper removal from the water column satisfies the criterion of rapid removal of 70% dissolved copper removal in 28 days;

·   For an experimental freshwater mesocosm study, carried out with a range of copper loadings (Schaeferset al.,2003), the measured data demonstrate a half life of 4 days and thus satisfy the criterion of rapid removal of copper (i.e. greater than 70% in 28 days);

·   For the whole-lake spike addition studies (LakeCourtilleand Saint Germain les Belles Reservoir), TICKET-UWM results, in concert with the measured data, indicate rapid removal of copper (i.e. greater than 70% in 28 days) for both lake systems;

·   Hypothetical TICKET-UWM simulations modeling the removal of copper in the MELIMEX limno-corrals following termination of copper loading demonstrate copper removal that does not meet the rapid removal benchmark because of a low settling velocity, low distribution coefficient, and low suspended solids concentration. 

Considering that the MILIMEX system is the only scenario that could not demonstrate ‘rapid removal’ it is critical to assess the environmental relevance of the MILIMEX system. The MILIMEX System was characterised by a setting velocity that is 10 times lower then the one in the EUSES system (0.2 versus 2.5 m/d) and a suspended solid concentration that is almost 3 times lower then the EUSES system (5.9 vesrus 16 mg/L). It is therefore concluded that the MILIMEX study was carried out under extreme conditions.

From Raderet al.,2013, it can therefore be concluded that under ‘environmental relevant’conditions, copper-ions are rapidly removed from the water-column.

This information is relevant to the environmental classification.

-In the sediment compartment,copper binds to the sediment organic carbon (particulate and dissolved) and to the anareobic sulphides, resulting in the formation of CuS. CuS has a very low stability constants/solubility limit (LogK=-41 (Di Toroet al.,1990) – see sectionadsorption/desorption) and therefore the ‘insoluble’ CuS keeps copper in the anaerobic sediment layers, limiting the potential for remobilization of Cu-ions into the water column.

To examine the potential for remobilization of copper from sediments, a series of 1-year simulations were performed, using the TICKET-UWM. These focused on re-suspension, diffusion, and burial to/from the sediment layer, their net effect on copper concentrations in the water column and changes in speciation in the sediment. Simulations were made with an oxic sediment layer as well as with an anoxic sediment layer (with varying concentrations of Acid Volatile Sulfides (AVS)) and varying re-suspension rates (up to 10 times the default EUSES model lake value).

In simulated sediments with AVS present in excess of copper, essentially all copper in sediment was present as copper sulfide because the affinity of copper for sulfides is much larger than the affinity for Organic Carbon.  CuS has a very low solubility product constant (Kps) and therefore, full copper sulfide precipitation was generally demonstrated : in all cases where AVS >1 µmol (reasonable worst case AVS concentration in European surface waters) and at environmentally relevant copper concentrations (< 0.1mg/L). As a result of this strong binding, the sediment log Kd greatly exceeded the water column log Kd and the net diffusive flux of copper was directed into the sediment. For anoxic sediments devoid of AVS and for oxic sediments, the net diffusive flux was small and directed out of the sediment. However, for all cases considered, the pseudo steady-state total and dissolved copper concentrations were at least 8 times lower than the concentration corresponding to conditions of 70% removal from the water column (see conditions detailed above).

Simpson et al (1998) and Sundelin and Erikson (2001) (see sectionadsorption/desorption)provide field evidence on the stability of the CuS binding :

·       Simpson et al (1998) investigated the oxidation rates of model metal sulfide phases to provide mechanistic information for interpreting the observations on natural sediments. CuS phases were kinetically stable over periods of several hours.

·       Sundelin and Erikson (2001) provide further evidence that, after long term oxygenation of sediment cores (3 to 7 months) Cu remains comparatively unavailable.

Last but not least, the assessment of 2 field experiments with intermittent copper dosing (LakeCourtille and the Saint Germain les Belles Reservoir lakes, yearly dosed with copper), assessed in Raderet al.,2013, provides further support for the absence of re-mobilization. Since both waterbodies are shallow, polymictic lakes, wind-driven resuspension is expected to play a role in copper dynamics in the water column. Neverteless, even if long-term resuspension does in fact occur, for both waterbodies, > 70% removal in less then 28 days was observed. The information therefore validates the results from the model simulations and absence of remobilization from the water column (Rader et al., 2013).

-In soils,decreases in copper solubility and in copper bio-availability are observed following copper spiking in the laboratory and from long-term field copper exposure experiments. Short term attenuation and long term ageing of copper, spiked in soluble forms to soils was demonstrated from laboratory and field experiments (Maet al.,2006a and 2006b) and reported in the section ‘adsorption/desorption’.

The soil environmental factors governing short term attenuation and ageing rates are soil pH, organic matter content, incubation time and temperature with soil pH being the key factor for ageing of Cu added to soils. From a range of laboratory and field experiments an ageing factor of 2 was derived as a reasonable worst case when considering field exposure data. This information is relevant to the soil PNEC derivation.

Transport and distribution

Relevant partitioning coefficients are available from literature.

-Aquatic compartment

Partition coefficient in freshwater suspended matter    Kpsusp= 30,246 l/kg (log Kp (pm/w) = 4.48) (50thpercentile)

Partition coefficient in freshwater sediment           Kpsed = 24,409 l/kg (log Kp(sed/w) = 4.39) (50th percentile)

Partition coefficient in estuarine suspended matter      Kpsusp= 56,234 l/kg (log Kp (pm/w) = 4.75) (50thpercentile)

Partition coefficient in marine suspended matter       Kpsusp= 131,826 l/kg (log Kp (pm/w) = 5.12) (50thpercentile)

-Terrestrial compartment

Partitioning coefficient                         Kd value soil: 2120 L/kg(log Kp (pm/w) = 3.33) (50thpercentile)

Bioaccumulation

Because copper is an essential nutrient, all living organisms have well developed mechanisms for regulating copper intake, copper elimination and internal copper binding. The information in the accumulation section demonstrates that copper is well regulated in all living organisms and that highest/ BAF values are noted when copper concentrations in water, sediments and soils are low and for organisms/ life stages with high nutritional needs. The/ BAF values therefore have no ecotoxicological meaning. It should be mentioned that the non-applicability of BCFs for metal and especially for essential metals was already recognized in the regulatory framework of aquatic hazard classification (OECD,2001).

Importantly, the literature review demonstrates that copper is not biomagnified in aquatic or terrestrial ecosystems.

The section further includes critical data related to (1) the accumulation of copper on critical target tissues (e.g. gills in aquatic organisms); (2) the influence of environmental parameters (e.g. Organic Carbon, pH, Cationic Exchange Capacity) as well as food intake on the accumulation of copper. This information is relevant to the understanding of the accumulation as well as the mechanism of actions, described in the sectionecotoxicological information

More detailed summaries on respectively aquatic and terrestrial bioaccumulation are available from the aquatic and terrestrial bioaccumulation summary sections

Information relevant to assessing copper toxicity from dietary exposure - of relevance to secondary poisoning assessments - is included in the section ‘ecotoxicological information’.

The summary record “ecotoxicological information” further provides an overall summary of the rational for the absence of bio-accumulation and no-concern for secondary poisoning.