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

Adsorption / desorption

Description of key information

According to transformation/dissolution study (OECD guidance 29) conducted for the substance the most critical constituents leachable to water from this UVCB substance are lead and zinc compounds. Therefore, the environmental fate and pathways focuses on the properties of these constituents and the key values for CSA are selected based on the read-across data on the most bioavailable compounds of Pb and Zn. The key values below are for Pb.

Key value for chemical safety assessment

Koc at 20 °C:

295

Other adsorption coefficients

Type:

log Kp (suspended matter-water)

Value in L/kg:

5.47

at the temperature of:

25 °C

Other adsorption coefficients

Type:

log Kp (sediment-water)

Value in L/kg:

5.19

at the temperature of:

25 °C

Other adsorption coefficients

Type:

log Kp (soil-water)

Value in L/kg:

6.4

at the temperature of:

25 °C

Additional information

The environmental hazard assessment was conducted based on the most critical constituents of the substance based on the transformation/dissolution study (OECD guidance 29) conducted for the target substance. 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 (75.4µg/L, silver (34.7 µg/L), cadmium (0.48 µg/L) and copper (17.2 µg/L). The 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. All read-across data for fate properties are based on test data using either soluble Pb or Zn salts or measured (dissolved) Pb or Zn concentrations. The weight of evidence approach was used to make conclusions on the key value for CSA.

For metals, adsorption/desorption translates in the distribution of the metals between the different fractions of the environmental compartment, e. g. the water (dissolved fraction, fraction bound to suspended matter), soil (fraction bound or complexed to the soil particles, fraction in the soil pore water). This distribution between the different compartments is translated in the partition coefficients between these different fractions. The log values for lead and zinc and their compounds are model values compiled from literature.

Adsorption and desorption properties of lead and its compounds

Freshwater environment

Partitioning coefficient for Pb between the freshwater and suspended particulate matter (SPM) are summarized in the voluntary risk assessment of lead (LDAI, 2008). An overview of the selected data is provided in the Table below.

Reported log K_D,SPM values for Pb in freshwaters in Europe.

Location	Log KD(L/kg)	Remarks	Reference
Four Dutch Lakes	6.0	average	Koelmans and Radovanovic, 1998
Calder River, UK Nidd River, UK Swale River, UK Trent River, UK All rivers All rivers	4.45 - 5.98 4.69 - 6.25 4.58 - 6.20 4.61 - 6.06 5.41 5.71	min-max range min-max range min-max range min-max range observed mean predicted mean	Lofts and Tipping, 2000
Scheldt, Belgium	5.3	salinity of 1.5 ppm	Nolting et al., 1999
Po River, Italy	5.5	median value	Pettine et al., 1994
Dutch freshwater	5.81	mean	Stortelder et al., 1989; in Crommentuyn et al., 1997
Upland-influenced river water, UK Low-salinity water, UK	4.6 5.5	modelled value modelled value	Tipping et al., 1998
7 freshwater locations in The Netherlands	5.93		Venema, 1994; in Crommentuyn et al., 1997
54 Czech rivers / 119 locations	5.44 5.18	median KD median KA^(1)	Veselý et al., 2001
RANGE	4.45 – 6.25

⁽¹⁾K_A: based on the acid soluble concentration

For the calculation of local and regional exposure concentrations the median log K_D,SPM value of 5.47 is selected. This value corresponds with a K_D,SPMof 295 121 l/kg.

For freshwater sediments, the selected K_Dvalue was 153 848 L/kg (Log K_D: 5.19).

Estuarine environment:

The next table summarizes the K_D,SPM values for suspended particulate matter that were determined in estuarine water bodies. The lowest reported logK_D (3.8) was found in a Texan estuary (Benoit et al, 1994). Other values are generally situated between 5.8 and 6.5 with a maximum value of 7.46 (Zhou et al, 2003). However, this value was calculated based on values of suspended particles derived from a graph. Also dissolved Pb was around or beneath detection level, the detection limit was used to calculate the partition coefficient. K_D values for this study are thus unreliable estimates. These values were therefore not taken into account while calculating the probability distribution. The maximum value can be found in North Australian estuaries with a K_D of 7.2 (Munksgaard and Parry, 2001).

Reported K_D,SPM values for Pb is estuarine surface waters.

Location	Log KD(L/kg)	Remarks	Reference
Seine estuary	6.1-6.3	Min-max range	Chiffoleau et al, 1994
Rhine estuary	5.85-6.26	Min-max value	Golimowski et al, 1990
Weser estuary, Germany	5.87-6.27	Different metal extraction methods used	Turner et al, 1992
Mersey estuary, UK	4.7-5.0	Estimated KDfor river water	Turner et al, 2002
Scheldt estuary, Belgium	6.0-6.51	Min-max value	Valenta et al, 1986
Scheldt estuary, Belgium	5.4-6.0	Min-max value	Baeyens, 1998
Penze estuary, France	5.5-6.8	Min-max value	Waeles et al, 2007
Mersey estuary, UK	5.0-5.48	Min-max value with increasing salinity	Hartnett & Berry, 2010
Conway estuary, Wales	5.62-7.46 ^1	Min-max range	Zhou et al, 2003
S. Baltic Sea	6.67	Median value	Sokolowski et al, 2001
N. Australia	5.5-7.2	Min-max value	Munksgaard and Parry, 2001
Lena estuary, Russia	6.42	Median value	Martin et al, 1993
Texas	3.8-6.8	Min-max value	Benoit et al, 1994
Danshuei estuary, Taiwan	5.2-6.5	Min-max value	Jiann et al, 2005
Nile estuary	5.2-5.3	Min-max value	Abdel-Moati, 1990
RANGE	3.8-7.46

¹ Values were calculated based on reported dissolved and particulate Pb-concentrations

For the calculation of local and regional exposure concentrations in estuarine environments, a median log K_D,SPM value of 5.83 should be used.This value corresponds with a K_D,SPM of 677 954 L/kg.

Marine environment:

A median K_D,SPM for Pb was calculated for suspended particulate matter in the marine environment, using the data given below. Four reported marine log K_D,SPM values were below 5,0 and were representative for the Atlantic Ocean, the Adriatic Sea, the Greek coast near Lesbos and the Scheldt estuary (4.7, 4.8, 4.1 and 4.9, respectively). Log K_D,SPM values for the North Sea are situated between 5.0 and 7.25. The maximum value is situated in the Adriatic Sea (log K_D,SPMof 7.8). All reported log K_D,SPM for other marine water bodies were situated between 5.0 and 7.8.

From a distribution (Triangular) that is fitted through all these data points a median log K_D,SPM of 6.18 for Pb in the marine environment is derived. This corresponds with a K_D,SPM of 1 518 099 L/kg.   

Reported log K_D,SPM values for Pb in marine surface water

Location	Log KD(L/kg)	Remarks	Reference
Belgian coastal waters	5.30-5.60	Min-max range	Baeyens et al, 1987
North Sea coastal waters	5.0-7.0	Min-max range	Balls, 1989
Scottish Sea Loch	6.47	Average value of 3 sampling stations	Hall et al
Southern North Sea	5.9-7.1^2	Min-max range, NSP-data	McManus and Prandle, 1996
Dover strait	5.71^2	Summer/winter value
Northern North Sea	6.68^2	Late summer
Humber/Wash, UK	6.53^2	Winter/spring
Humber/Wash, UK	7.24^2	Summer
Scheldt, Belgium	4.9	Salinity of 30 ppm	Nolting et al, 1999
Baltic Sea	5.78^2 6.49^2 7.10^2	10^thpercentile 50^thpercentile 90^thpercentile	Pohl and Hennings, 1999
North Sea	5.51^2 6.30^2 7.25^2	10^thpercentile 50^thpercentile 90^thpercentile	Tappin et al, 1995
Seawater, UK	6.2	Modeled value	Tipping et al, 1998
Oceans	6.3-6.5	Min-max range	Valenta at al, 1986
Mytilene, Greek coast	4.1	Calculated value	Angelidis et al, 2003
Adriatic Sea	4.8-7.8	Min-max range	Tankéré et al, 2001
Black Sea	5.9-6.6	Min-max range	Tankéré et al, 2001
Atlantic Ocean	4.7-6.4	Min-max range	Helmers, 1996
RANGE	4.1-7.8

²Values and/or percentiles were calculated based on reported dissolved and particulate Pb-concentrations

For the marine environment, only one study has reported Pb partition coefficients between the aqueous phase (overlying water) and sediment (Yland et al, 1996). They reported for sediments from the North Sea and Wadden Sea a log K_D of 5.66.

Terrestrial environment

The best estimates of K_Ds to assess leaching losses of Pb from the soil are made by models based on in situ pore water concentrations. Adsorption K_Ds do not take into account ageing reactions while K_Ds measured in dilute salt extracts tend to underestimate the Pb concentrations in pore water as the ionic strength is usually lower in the extracts than in the pore water. Measurement of Pb concentrations in pore water overcomes these shortcomings. There are only two studies available where K_Ds are measured based on pore water Pb concentrations (de Groot et al., 1998; Smolders et al., 2000). If the regression models are applied to predict the K_D of a “typical” soil with pH 6.5, 2 % organic matter content and 27.4 mg Pb/kg soil, the model of de Groot predicts a K_D of 19 10³L/kg (Al-ox = 34 mmol kg^-1, %fraction 2-38 µm = 12) while the model of Smolders predicts a K_D of 1.8 10³L/kg. If the pH decreases to 3.5 the K_Ds decrease to 6.9 10² and 2.2 10² L/kg respectively, if the pH increases to 7.5 the K_Ds increase to 58 10³ and 3.5 10³ L/kg respectively. It is difficult to derive one “typical” realistic K_D based on these two equations. Therefore the average of the median measured K_Ds (see Table below) by de Groot et al. (1998) and Smolders et al (2000), i.e. 6,400 L/kg, can be used as a realistic K_D to calculate Pb leaching losses. A realistic low K_D is 6.0 10² L/kg (10^th percentile of the combined K_D datasets of de Groot and Smolders), a realistic high K_D is 43 10³ L/kg (90^th percentile of the combined K_D datasets).

Regression models of K_Das a function of soil parameters.

KDregression model	Notes	Reference
logKD= -0.13 + 0.48 pH +0.16 log(%fraction 2-38 µm) + 0.73 log(Al-ox)	r² = 0.84,in situKD, n=47, contaminated and uncontaminated soils from NL, B and D	de Groot et al., 1998
logKD= 0.22 + 0.75 log[Pb]tot+0.30 pH	r² = 0.94,in situKD, n=13, contaminated soils from B	Smolders et al., 2000
logKD= 0.28 pH + log(%OM) + 1.0	r² = 0.38, adsorption KDin 0.005N salts, n=33, contaminated and uncontaminated soils from NL, UK and F	Gerritse & Van Driel, 1984
log[Pb]s= -0.34 – 0.15 pH + 0.61 log(%OM*10)	r² = 0.37, metal concentration in water extract, n=31, contaminated and uncontaminated soils from NL, UK and F	McBride et al., 1997
log[Pb]tot- 0.988 log[Pb]s= 1.30 + 0.55 pH	metal concentration in 0.005 M CaCl2+ 0.005 M Ca(NO3)2extract, n=100, contaminated soils from UK	Jopony & Young, 1994
logKD= 0.37 pH + 0.44 log[Pb]tot+ 1.19	r² = 0.56, compilation of >70 studies, n=204	Sauvé et al., 2000

%OM: percentage organic matter in the soil; [Pb]_s: Pb concentration in solution; [Pb]_tot: total Pb concentration in the soil, Al-ox: amount of aluminum extracted by ammonium oxalate/oxalic acid, %OC: percentage organic carbon content.

 

The following information is taken into account for any environmental exposure assessment:

From the literature overview, the following partitioning coefficients have been derived for Pb:    

Aquatic compartment

Partition coefficient in freshwater suspended matter: Kd_susp= 295 121 L/kg

Partition coefficient in freshwater sediment: Kd_sed,fw = 153 848 L/kg

Partition coefficient in marine sediment: Kd_sed,mar = 457 088 L/kg

Partition coefficient in estuarine suspended matter: Kd_susp= 667 954 L/kg

Partition coefficient in marine suspended matter: Kd,_susp= 1 518 099 L/kg

Soil compartment

Partitioning coefficient: Kd value soil: 6 400 L/kg

Absorption and desorption properties of zinc and its compounds

The study records on partition coefficients are given under IUCLID section 5.6 "Additional environmental data" and summarized below.

For metals, adsorption/desorption translates in the distribution of the metals between the different fractions of the environmental compartment, e.g. the water (dissolved fraction, fraction bound to suspended matter), soil (fraction bound or complexed to the soil particles, fraction in the soil pore water). This distribution between the different compartments is translated in the partition coefficients between these different fractions.

Partition coefficients for zinc in freshwater has been reviewed in the RAR (ECB 2008). Based on the extensive experimental evidence, a partition coefficient for the distribution between solid particulate matter and water (Kpsusp) of 5.04 (log value) has been defined for EU waters and used throughout the RAR. The Kp for the distribution between sediment and water (Kp_sed) was estimated in the RAR from that for particulate matter, as follows: Kp_sed= Kp_susp/ 1.5, based on the average difference in concentrations of zinc and other metals in both media. For zinc this results in a Kp_sedof 73 000 l/kg (log value: 4.86). (ECB 2008)

The marine Kd was derived based on data from several marine waters. The geomean value for zinc in seawater is 6010 l/kg

For soil, a solids-water partitioning coefficient of 158.5 l/kg (log value 2.2) was determined experimentally on 11 American soils.This value was used in the RA Zinc.

Conclusion on the adsoprtion potential of the target substance

The chemical safety assessment of the target substance focuses on the most critical and bioavailable constituents of the substance which were determined based on the transformation and dissolution study (OECD guidance 29). According to T/D study results, the most soluble and critical components of this substance are lead and zinc.

Partition coefficient in freshwater suspended matter:

• log Kpsusp (Zn) = 5.04 l/kg

• log Kpsusp (Pb)= 5.47 l/kg

Partition coefficient in freshwater sediment:

• log Kpsed (Zn)= 4.86 l/kg

• log Kpsed (Pb)= 5.19 l/kg

Partition coefficient in marine sediment:

• log Kd sed (Zn)= log 3.78 l/kg

• log Kpsed (Pb) = Log 5.66 l/kg

Partition coefficient in marine suspended matter:

• log Kp, susp (Pb) = Log 6.18 l/kg

Partition coefficient in soil compartment:

• log Kd value for soil (Zn) = 2.2 l/kg

• log Kd value soil (Pb) = 3.81 l/kg

[LogKoc: 5.47]