Concentrates of lead and zinc compounds with sulfur resulting from hydrometallurgy (hot acid leaching, super-hot acid leaching and flotation)

Bioaccumulation: aquatic / sediment

Description of key information

Based on the T/D study results and the toxicity profile and bioaccumulation properties of the critical constituents, lead was considered to be the most critical constituent of the target substance, and the key value for CSA was selected based on the read-across data on the bioaccumulation/bioconcentration factors of lead in freshwater.

Key value for chemical safety assessment

BCF (aquatic species):

1 553 L/kg ww

Additional information

The environmental hazard assessment was conducted based on the most critical constituents of the target substance which were determined by using the transformation/dissolution study (OECD guidance 29). According to the chemical composition analysis, the main phases of the substance are lead sulphate and zinc sulphide. The product consists primarily of sulphur (ca. 35 %), lead (ca. 25 %) and zinc (ca. 17 %) together with minor trace elements such as silver, silicon, aluminium, calcium and iron.

The transformation and dissolution study (OECD guidance 29) results indicated that the release at pH 6 was higher for all studied elements compared to release at pH 8. Based on the screening test results (loading rate 100 mg/L), the readily soluble was lead with release of 8282 µg/L. and 75.4 µg/L, respectively. The other minor leachable metals were zinc (75.4 µg/L, silver (34.7 µg/L), cadmium (0.48 µg/L) and copper (17.2 µg/L). In the 28 day test with lower loading rate (1 mg/L, pH 6), only concentrations of Pb (362.4 µg/L) and Zn (3.2 µg/L) were over the detection limits or blank sample values.

According to T/D study results, the most soluble and critical components of this substance are lead and zinc. Therefore, the studies for this endpoint have been selected as a read-across data for the critical constituents. The read-across justification is presented in CSR annex I.

Based on the toxicity profile and the bioaccumulation properties of the soluble constituents of the target substance, bioaccumulation was not considered relevant for essential element, zinc, because of the general presence of homeostatic control mechanisms.

McGeer et al (2003) recently extensively the reviewed evidence on bioconcentration and bioaccumulation of zinc as a function of exposure concentration in a number of taxonomic groups (algae, molluscs, arthropods, annelids, salmonid fish, cyprinid fish, and other fish). The data clearly illustrated that internal zinc content is well regulated. All eight species taxonomic groups investigated exhibited very slight increases in whole body concentration over a dramatic increase in exposure concentration. In fact, most species did not show significant increases in zinc accumulation when exposure levels increased, even when exposure concentrations reached those that would be predicted to cause chronic effects. This suggests that adverse effects related to Zn exposure are independent of whole body accumulation. Due to the general lack of increased whole body and tissue concentrations at higher exposure levels, the zinc BCF data showed an inverse relationship to exposure concentrations. In all cases, the relationship of BCF to exposure was significant and negative. The slopes of the BCF/BAF – exposure relations were: algae: -1.0, insects: -0.79, arthropods: -0.73, molluscs: -0.83, salmonids: -0.92, Centrarchids: -0.80, Killifish: -0.84, other fish: -0.87. Overall, species mean slope was -0.85 +/- 0.03 (McGeer et al 2003). The study records supporting these findings are presented in IUCLID section 5.3.1 & 5.3.2.

The physiological basis for the inverse relationship of BCF to zinc exposure concentration arises from Zn uptake and control mechanisms. At low environmental zinc levels, organisms are able to sequester and retain Zn in tissues for essential functions. When Zn exposure is more elevated, aquatic organisms are able to control uptake. There is clear evidence that many species actively regulate their body Zn concentrations, including crustaceae, oligochaetes, mussels, gastropods, fish, amphipods, chironomids by different mechanisms (McGeer et al 2003).

On the other hand, since lead is carcinogenic, reproduction toxic and has repeated dose toxicity, all read-across data for bioaccumulation in aquatic and terrestrial compartments are based on test data using either soluble Pb salts or measured (dissolved) Pb from the field monitoring. The weight of evidence approach was used to make conclusions on the key value for CSA.

Bioaccumulation of the most critical constituent (lead)

Bioconcentration (BCFs) and bioaccumulation factors (BAFs) for Pb from water to aquatic invertebrates and fish have been summarized in the voluntary risk assessment of lead, VRAL (LDAI, 2008).

Based on the VRAL, within typical environmental concentration range, the gathered BAFs for fish ranged between 11 and 143 L/kgww (10 – 90th%) with a median value of 23 L/kgww, while the BAFs for molluscs ranged between 18 and 3,850 L/kgww (median value of 675 L/kgww), for insects between 968 and 4,740 L/kgww (median value of 1,830 L/kgww) and for crustaceans between 1,583 and 11,260 L/kgww (median value of 3,440 L/kgww). The following table presents an overview of the bioaccumulation in freshwater.

The range of bioaccumulation factor (BAF in L/kgww) of Pb in freshwater organisms.

Diet	Variable	10^th%	50^th%	90^th%	n
Crustaceans	All exposures	1 187	3 159	10 570	8
	0.18-15 µg/L	1 583	3 440	11 260	7
Molluscs	All exposures	11	473	3 535	14
	0.18-15 µg/L	18	675	3 850	11
Annelids	All exposures	1 620	1 620	1 620	1
	0.18-15 µg/L	1 620	1 620	1 620	1
Acarides	All exposures	1 730	1 730	1 730	1
	0.18-15 µg/L	1 730	1 730	1 730	1
Insects	All exposures	968	1 830	4 740	7
	0.18-15 µg/L	968	1 830	4 740	7
Fish	All exposures	11	24	245	16
	0.18-15 µg/L	11	23	143	16

According to the VRAL (2008) a mixed diet scenario is assumed, considering that birds/mammals consume equal proportion of the different food types. Based on significant high bioaccumulation in molluscs, secondary poisoning was also considered for a “mollusc food chain”.

The range of bioaccumulation factor (BAF in L/kg_ww) of Pb in the mixed and mollusc food diet is presented below.

The range of bioaccumulation factor (BAF in L/kg_ww) of Pb in the mixed diet.

Diet	variable	10^th%	50^th%	90^th%	n
Mixed food diet	All exposures	921	1 472	3 740	49
	0.18-15 µg/L	988	1 553	3 890	44
Mollusc food diet	All exposures	11	473	3 535	14
	0.18-15 µg/L	18	675	3 850	11

The table shows that the 50^th% of the mixed diet BAF for aquatic organisms is 1 553 L/kg (90^th%: 3,890 L/kg) and that the mixed diet scenario is driven by the BAF values retrieved from the invertebrates. The 50^th% BAF of the mollusc food diet is somewhat lower, i. e. 675 l/kg (90^th%: 3 850 L/kg).

The key value selected for CSA in freshwater is BAF value of 1553 L/kg, and this value is used for the environmental ES&RC of the target substance.