Zinc, desilverizing skims

Endpoint summary

Additional information

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4. ENVIRONMENTAL FATE PROPERTIE

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. 

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.”

Relevant fate aspects for copper in the environment have been included in the section “additional information on fate and pathways” and are summarized below.

As outlined in theguidance (2009 & 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/dissolution of Cu°

Copper in its metallic form (Cu°) needs to be transformed to its ionic forms to become available for uptake by living organisms and therefore the rate and extend of the transformation/dissolution of copper in its massive and powder forms have been assessed from transformation/dissolution tests (in accordance to the OECD guidance, Annex 10 of the GHS).

The results of the transformation/dissolution tests are described in details in “additional information fate and pathways” and are summarized as follows

For massive copper materials, seven days transformation/dissolution tests were carried out at pH 6, 7 and 8, in accordance to the OECD guidelines (Annex 10 of GHS) using different surface loadings (Rodriguez et al, 2007, 2011 and 2012) – record in section “additional information on environmental fate and pathways”). The results were used to derive the release of copper-ions from 1 mm particles at loadings of 1,10 and 100mg/L.

·        Rodriguez et al., 2007 assessed the need for classification of pure massive copper materials and tested, during 7 and 28 days T/D tests, copper releases from copper wire pieces (99.9% purity) with varying diameters. The tests were carried out with various mass loadings (1-100 mg/l), surface area loadings (1-281 mm²/l) and covering pH 6-8. 

The data demonstrated that

- Copper releases during the transformation/dissolution tests were dependent on the stirring rate. At high stirring rates (>50 rpm), copper release increases exponentially and high intra- and inter-vessel variability in measured dissolved copper concentrations were observed. Considering that this increased release and variability was related to particle abrasion, and particle abrasion should be prevented (GHS rev. 4, 2011, Annex 10, A10.2.3.1), only release rates from tests at 50 rpm were further considered.

- Copper releases during transformation/dissolution tests are pH dependent and 6 times higher releases were measured at pH 6 compared to pH 7 and 8.

- Copper releases during transformation/dissolution tests are related to the surface loading tested (mm²/l). The average surface–specific copper release (µg dissolved Cu /mm²exposed) for respectively 7 (acute) and 28 (chronic) dissolution/transformation tests are:

* 1.15 µg Cu/ mm²after7 days T/D tests at pH 6

* 0.13 µg Cu/mm²after7 days T/D tests at pH 7

*  0.1 9 µg Cu/mm²after7 days T/D tests at pH 8.  

* 4.2 µg Cu/mm²after 28 days T/D test at pH 6 (excluding one outlier).

Since the GHS and CLP agreed on a default value of 1 mm particles for the massive classification , the surface loading applicable to a 1mm particle at various mass loadings (1-100 mg/l) was calculated. Following this methodology, for copper with a density is 8.9 g/cm³, at a loading of 1 mg/L, the surface loading for a 1 mm particle corresponds to 0.67 mm²/L. The surface loading approach avoids issues associated with the selection of a given particle type or preparation of particles specifically for classification purposes (non-commercial particles) and allows easy and precise measurements of the surface area. 

 

·        To ensure consistency with the GHS guidance (stirring at 100 rpm, without causing abrasion of particles), Rodriguezet al., 2011 and 2012 avoided abrasion of the particles to the test vessels by applying distinct non-abrasion devices: copper wires mounted in polypropylene disks and copper massive samples mounted in epoxy and polished. The lowest coefficient of variations were obtained for copper massive samples mounted in epoxy and polished and the results from these tests were retained for classification purposes. The non-abrasion device (epoxy mounted) resulted in the following surface-specific copper releases:

o   0.41 µg Cu/mm² after7 days T/D tests at 47 mm2/L, pH 6 (Rodriguezet al., 2011)

o   1.5 µg Cu/mm² after7 days T/D tests at 0.67 mm2/L, pH 6 (Rodriguezet al., 2012)

o   5.0 µg Cu/mm²after 28 days T/D test at 0.67 mm2/L, pH 6 (Rodriguezet al., 2012)

The results at a surface loading of 0.67 mm2/L (Rodriguezet al., 2012) are retained for the classification of copper massive (particles of 1 mm at loading of 1mg/L corresponds to a surface loading of 0.67 mm2/L):

o   1 µg dissolved Cu/L released after7 days T/D tests at 1mg/L , 0.67 mm2/L, pH 6 (copper release rate of 1.5 µg Cu/7 days.mm²)

o   3.4 µg dissolved Cu/L released after 28 days T/D test at 1mg/L , 0.67 mm2/L, pH 6 (copper release rate of 5.0 µg Cu/28 days. mm²)

For Copper powders, relevant records on transformation/dissolution tests are reported in section “additional information on environmental fate and pathways”.

The surface area’s of copper powders (10 µm – 1 mm), assumed to be spheres, theroretically range between 67.5 and 0.67mm²/mg. The surface area of a fine representative powder was measured as 48 mm²/mg (measured by sieving) and 107 mm²/mg (measured by sieving and BET)( Skeaff and Hardy, 2005). 

Following the surface loading approach , copper release rates for reasonable worst case powder surface loadings of 67.5 and 107 mm2/L is used for the classification of copper powders at 1 mg/L mass loading.

Skeaff and Hardy, 2005 (available from VRAR, 2008) performed T/D tests (7 days at pH6) on the fine representative copper powder sample (48 mm²/mg (measured by sieving) and 107 mm²/mg (measured by sieving and BET)) at loadings of 1 and 100 mg/l. The data can be summarized as:

 

o    The measured release of copper to the aqueous medium at 7 days for the 1 mg/l loading at pH 6, was 82 µg/l. The ratio of dissolved copper to solid copper at 7 days (1 mg/l; pH6) was 0.079.

o    The 1 and 100 mg/l mass loadings correspond to surface area loadings, A_calc, of 50 and 4800 mm²/l. The 7 days data for the five tests with the copper powders corresponded to the non-linear equation:

o   The author mentioned that part of the observed release may have been related to abrasion of the particles 

·        The surface area-specific release rate measured by Rodriguez et al.,2007 and 2011 are considered as relevant for read-across to copper powder                                                                                                           

7 days transformation/dissolution

·        The results from the 7 days non-abrasive T/D test set-up, at pH 6 and loading of 47 mm²/L (Rodriguez et al.,2011) are retained for read-across to powders T/D at loadings of 1 mg/L (67-107 mm2/L) . The obtained surface specific release rate of 0.41 µg Cu/mm² results in a copper release from copper powders at a mass loading of 1 mg/L and corresponding surface loading of 67.5 and 107 mm²/L of 0.028 – 0.044 mg Cu/L (pH 6).  Comparison of the release at 107 mm2/L with the release measured y Skeaff and Hardy, 2005 indicates that abrasion during the T/D test performed by Skeaff and Hardy did influence the data (factor 2 difference).

·        At pH 7 and 8, the results from the 7 days T/D test data from Rodriguez et al., 2007 can be used as a worst case (with abrasion). The obtained surface specific release rate of 0.19 µg Cu/mm²(pH 7) and 0.13µg Cu/mm² (pH 8) results in a copper release from copper powders at a mass loading of 1 mg/L and corresponding surface loading of 67.5 and 107 mm²/L of of respectively 0.013-0.021 mg Cu/L (pH 7) and 0.009-0.014 mg Cu/L (pH 8)

28 days transformation/dissolution

·        The release rates after 28 days T/D were calculated following linear extrapolation of the above retained 7 days transformation/dissolution test results : 0.112-0.176 mg Cu/L (pH 6), 0.051-0.084 mg Cu/L (pH 7) and 0.035-0.056 mg Cu/L (pH 8). The release data at pH 7 and 8 include particle abrasion.

The Table below summarizes the the available transformation/ dissolution data

The following copper releases are retained for classification :

·        7 days, pH 6 : non abrasion data from Rodriguez et al.,2011 : a copper release at 1mg/l of 0.028 – 0.044 mg Cu/L. 

·        7 days,  pH7 : Rodriguez et al, 2007 : a copper release at 1mg/l of 0.013-0.021 mg Cu/L (includes abrasion) 

·        7 days,  pH 8 : Rodriguez et al, 2007 : a copper release at 1mg/l of 0.009-0.014 mg Cu/L (includes abrasion) 

·        28 days T/D were calculated following linear extrapolation of the obove retained 7 days transformation/dissolution test results : 0.112-0.176 mg Cu/L (pH 6), 0.051-0.084 mg Cu/L (pH 7) and 0.035-0.056 mg Cu/L (pH 8). The release data at pH 7 and 8 include particle abrasion.

Table: Summary of the transformation/dissolution results, relevant to copper powders. The underlined values are retained for the classification

Transformation/dissolution of fine copper powders
loading (mg/l)	loading (mm^2/l)	Time (Days)	mg dissolved Cu/l			comment
			At pH 6	At pH 7	At pH 8
1	47-107	7	0.082	-	-	Direct results of T/D of fine copper powder[1]- from Skeaff and Hardy, 2005.
1	67.5	7	0.098	-	-	Calculated T/D of 10 µm powder(^1) from  = 8.9246 (Skeaff and Hardy, 2005) See discussion below.*
1	67.5- 107	7	0.078-0.123	0.013-0.021	0.009-0.014	Calculated T/D of 10 µm powder3 from surface area-specific releases (Rodriguezet al., 2007).
1	67.5-107	7	0.028-0.044	-	-	Calculated T/D of 10 µm powder from non-abrasive T/D tests at 47 mm2/L, pH 6 , 0.41 µg Cu/mm2  (Rodriguezet al., 2011)
1	67.5-107	28	0.112-0.176*	0.051-0.084**(1)	0.035-0.056**(1)	Linear extrapolation between 7 and 28 days) :* fromRodriguezet al., 2011;** from Rodriguezet al., 2007

[1]Includes abrasion of the particles observed

 

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 (eg 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 maybe 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 Rader K.,2013 and described in the section “additional information on environmnetal fate and pathways”.

 

The assessment relies on modeling simulations, based on theTableau Input Coupled Kinetics Equilibrium Transport (TICKET) model (Farley et 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 (Schaefers et 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 Rader K., 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 Toro et 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.

 

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 Rader K., 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 K., 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 (Ma et 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         Kp_susp= 30,246 l/kg (log Kp (pm/w) = 4.48) (50^thpercentile)

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

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

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

 

-Terrestrial compartment

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

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 (eg gills in aquatic organisms); (2) the influence of environmental parameters (eg 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

The 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 n overall summary of the rational for the absence of bio-accumulation and no-concern for secondary poisoning.