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In assessing the ecotoxicity of metals in the various environmental compartments (aquatic, terrestrial and sediment), it is assumed that toxicity is not controlled by the total concentration of a metal, but by the bioavailable form. For metals, this bioavailable form is generally accepted to be the free metal-ion in solution. In the absence of speciation data and as a conservative approximation, it can also be assumed that the total soluble lead pool is bioavailable. All reliable data on ecotoxicity and environmental fate and behaviour of lead and lead substances were therefore selected based on soluble Pb salts or measured (dissolved) Pb concentration.


The reliable data selected for the environmental fate and behaviour of lead are all based on either monitoring data of prevailing lead concentrations in water, soil, sediment, suspended matter and organisms or on experimental resultswithlead (di)nitrate and lead chloride. All reliable data are expressed based on elemental Pb concentrations and grouped together in a read-across approach and will be used for all lead substances because upon dissolution of lead substances, the Pb-ion is the controlling adsorption and bioaccumulation.

Lead attenuation, removal from water column, geochemical cycling

As described above, after the release of Pb(II) in the environment, further transformations occur thereby changing the potential for toxicity, induced by the free Pb(II) ions. The concentrations of “active” Pb(II) 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 Lead 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 theTableau Input Coupled Kinetics Equilibrium Transport (TICKET) model – Unit World Model (UWM)for evaluating removal of soluble metal species through precipitation/partitioning processes over a range of environmentally relevant conditions have been assessed for evaluating the removal of soluble lead species. The information is reported in the section "additional information on environmental fate" and summarized below

-In the water compartment,leadis rapidly and strongly bound to the suspended solids of the water column. This binding and subsequent settling to the sediment allows for rapid metal removal of lead from the water column as demonstrated by a decrease in soluble lead concentrations by >70% in 28 days in a range of simulations according to the TICKET-UWM calculations (Rader et al., 2010). This information is reported in the section:additional information on environmental fateand is relevant to the environmental classification.

-In the sediment compartment,leadbinds to the anaerobic sulphides resulting in the formation of PbS. The analysis was based on an AVS concentration between 1 and 9 µmol AVS/g. The results show that “insoluble” PbS keeps lead in the anaerobic sediment layers, limiting the potential for remobilization of Pb-ions into the water column. The potential for remobilization from oxic sediments, quantified by comparing water column lead concentrations resulting from sediment feedback to the 70% removal concentration was also insignificant. For conditions favoring remobilization, water column dissolved lead concentrations at pseudo steady state were more than 100 times less than the 70% removal concentration. All these results therefore suggest that Pb is relatively insignificant and provide evidence that supports the removal of the “persistent” criterion for soluble lead salts. The relevant information is reported in the section“additional information on environmental fate”and is relevant to the environmental classification.