Registration Dossier

Environmental fate & pathways

Additional information on environmental fate and behaviour

Administrative data

Endpoint:
additional information on environmental fate and behaviour
Type of information:
other: report
Adequacy of study:
supporting study
Study period:
2012
Reliability:
2 (reliable with restrictions)
Cross-reference
Reason / purpose:
reference to same study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2012

Materials and methods

Test guideline
Guideline:
other: Unit World Model
Principles of method if other than guideline:
A Unit World Model (UWM) is a typical Mackay-based screening level model capable of assessing the fate and effects of chemicals by the simultaneous consideration of chemical partitioning, transport, reactivity, bioavailability, sediment burial and re-suspension. A Unit World Model (UWM) has recently been developed specifically for metals, building on previous screening-level calculations that have been developed for organic contaminants.
Type of study / information:
modelling

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
1. Metals that readily methylate, such as Hg, Se and others
2. Metals that rapidly hydrolyze under a range of relevant aquatic conditions and that form different non-toxic chemical forms that precipitate in the water column, such as Fe, Sb, Mo, Al, Sn, Cr and others
3. Metals that partition and precipitate like the previous group, but for which the “irreversibility” (i.e. binding to a non-bioavailable form under a range of environmental conditions) needs to be proved. This group includes metals such as Cu, Zn, Ni, Co, Pb and others.

Results and discussion

Any other information on results incl. tables

A couple of issues and questions require attention and resolution in order to standardize the modelling and enable an assessment of the Rapid Removal from the water column to be made. These cover the following in particular:

A. Which metal loading rates should be used to conduct the calculations?

The 0.1 mg/l cut-off could be seen as a benchmark for the start of the assessment, given the loading point that would make a distinction between degradable and non-degradable substances.

B. What standard modelling conditions should be used to calculate the rapid removal rate?

See attachment Table 5a

C. What to use in case both modelled and measured KD values are available?

The philosophy embedded in the REACH and CLP guidance is that measured data, when relevant and reliable, are always preferred over modelled data, a principle that would apply equally here. On the other hand, standardization of approaches to determine partitioning provides a consistent approach for determining comparative hazard IDs, especially for those metals where empirical KD values are not available or are less reliable.

D. Rapid removal assessment based upon the loaded nominal or measured dissolved fraction?

There are consequently two three potential approaches for assessing metal removal:

1. The initial instantaneous removal of metal from the soluble phase to the particles counted toward the percentage removal (blue curve in Figure 2 attachment).

2. The initial instantaneous removal is ignored, and the percentage removal is counted based upon the further degradation of the dissolved fraction (red curve in Figure 2 attachment).

In analogy with organics, it is suggested to assess the rapid degradation rate, ignoring the instantaneous partitioning, thus based on the dissolved fraction.

E. Robustness of the remobilization evidence?

To increase the robustness of the evidence on “rapid removal and absence of remobilization” as equivalent to organic substances, the following additional information is to be considered:

- Di Toro et al., 2001 compared potential elemental concentrations in open ocean (as determined from the relative weathering of natural rock, run-off and dilution in open ocean) with actual metal concentrations in open oceans. For most elements (except e.g. Na and Ca) the authors observed that metal concentration in open oceans was four to six orders of magnitude lower than the predicted concentrations. This provides evidence that metal removal is a general process

- The solubility product of metal sulphides is very low , demonstrating their low solubility

- Ecotoxicity studies in the laboratory and the field have demonstrated that soluble metal ions are the driver for metal toxicity (BLM metals: Zn, Ni, Cu ..). For several metals, ecotoxicity studies have demonstrated that metal sulphides are not toxic (e.g. Cu, Zn ,Ni…) (McGrath et al. 2002).

- Laboratory studies and field evidence on rapid removal and/or lack of remobilization may be available (e.g. Cu and Zn) and used in a weight of evidence approach

Applicant's summary and conclusion

Conclusions:
A weight of evidence approach should be applied to interpret the overall outcome of the UWM model calculations.
” Factors that can be considered in the weight of evidence are differences between model runs – are they small or big? Do the modeled data match field experiments that show rapid removal from the water column? Are there laboratory experiments that confirm UWM outputs and show rapid removal from the water column?”