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Environmental fate & pathways

Adsorption / desorption

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Description of key information

For the risk assessment of the pigments, the Kd values for lead are used to estimate partitioning to suspended matter, sediment and soil.  

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (solids-water in suspended matter)
Value in L/kg:
5.47

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
5.19

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
3.81

Additional information

Data on adsorption of C.I. Pigment Yellow 34 and C.I. Pigment Red 104 are not available. However, chromate ions (CrO42-) and lead ions (Pb2+) may dissociate from the substance and adsorb to suspended particles and soil. Experimental and calculated log Kd-values for lead and chromium indicate that both moieties may adsorb to suspended particles and soil. However, the partitioning of lead and chromium depends on pH, Fe-oxide, mineral particles and DOC-contents of water and soil. At neutral pH lead mostly forms carbon-lead complexes, whereas at low pH lead exists predominantly in the more mobile ionic form. Soil pH has a comparable effect on chromium; with increasing pH the adsorption of chromium increases. Furthermore, at neutral pH CrO42- ions are expected to be reduced to the less mobile chromium III in the environment. The mobility of both ions decreases with increasing proportion of organic matter in soils.

The following log Kd values for lead (resulting from investigations for rivers (Lofts and Tipping, 2000)) were reported : 5.41 (observed) - 5.71 (predicted). For chromium the mean of calculated log Kd values for pH ranging from 2 -10 (from Sauve et al, 2000) was 4.17.

For the risk assessment, use is made of the extensive work carried out for the risk evaluations of chromium and lead at the EU level.The Kd values used for PEC and PNEC calculations for chromium (EU RAR) and lead (vRAR) are presented in the Table. When available, also Kd values given in the ECHA Guidance Appendix R.7.13 -2 Metals are included.

Substance

Type

Kd (L/kg)

remarks

Chromium (VI)

Kd (suspended matter – water)

2000

Acid conditions

 

 

200

Neutral-alkaline conditions

 

Kd (sediment – water)

1000

Acid conditions

 

 

100

Neutral-alkaline conditions

 

Kd (soil – water)

50

Acid conditions

 

 

2

Neutral-alkaline conditions

Chromium (III)

Kd (suspended matter – water)

30000

Acid conditions

 

 

300000

Neutral-alkaline conditions

 

Kd (sediment matter – water)

11000

Acid conditions

 

 

120000

Neutral-alkaline conditions

 

Kd (soil – water)

800

Acid conditions

 

 

15000

Neutral-alkaline conditions

 

 

 

 

Lead

Kd (suspended matter –water)

295121 L/kg

Freshwater data

50th percentile n= 12, from vRAR

(same value reported in REACH guidance Appendix R.7.13-2 Metals)

 

 

954993 L/kg

Estuarine data

50th percentile n= 19, from vRAR

 

 

1698244 L/kg

Marine data

50th percentile n= 22, from vRAR

 

Kd (sediment – water)

154882 L/kg

50th percentile n= 5 (REACH guidance Appendix R.7.13-2 Metals)

 

 

153848 L/kg

Average of two median Kd values derived from datasets with many measured background and ambient concentrations (vRAR)

 

Kd (soil – water)

6400 L/kg

50th percentile n= 60 (REACH guidance Appendix R.7.13-2 Metals)

 

 

6400 L/kg

Average of two median measured Kd, n= 60 from vRAR

Chromium

The Kd for chromium (VI) and chromium (III) are based on the available measured data. Kd could not be derived from a statistical distribution due to the lack of sufficient data. Instead the Rapporteur of the EU RAR selected the values by inspection of the available data set to reflect the available information under acid (pH < 5) and neutral-alkaline (pH > 6) conditions.

Lead

A large number of measured sorption data is available for lead. 10th, 50th and 90th percentile Kd have been derived from the fitted distributions in the vRAR. Median Kd have been used for the derivation of PEC and PNEC. This is in agreement with the REACH guidance in Appendix R.7.13-2: Environmental risk assessment for metals and metal compounds.

Kd suspended matter – water was determined separately for freshwater, estuarine and marine data for lead. The 10th, 50th, and 90th percentiles of the fitted distributions were reported in the vRAR lead. In line with REACH guidance the median values should be used for PEC and PNEC derivation. The 10th and 90th percentiles could be used for an uncertainty analysis.

Kd sediment is derived from the REACH Guidance document Appendix R.7.13 Metals, Table 7.13.2. A similar value was proposed for Kd sediment in the vRAR based on the average of two median Kd derived from respectively environmental concentration distributions for background or ambient lead concentrations in surface water and sediment (Kd sediment).

Similarly Kd soil was determined as the average of two medians derived from two data sets where Kd was based on measured concentrations of lead in pore water and Kd was normalised to a typical soil with pH 6.5, 2% organic matter content and 27.4 mgPb/kg soil.