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Environmental fate & pathways

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The hazard assessment of inorganic UVCBs for the purpose of classification and derivation of fate properties and safe effect thresholds (e.g. PNEC) is a cumbersome and complex process. Due to the intrinsic variability of the composition of an UVCB, it is difficult to select a sample that would unambiguously be representative for the (eco)toxicological hazard profile of the UVCB and could subsequently be used for testing. Instead of direct testing, a precautionary approach is taken where the UVCB is treated as a complex metal containing substance containing a number of discrete constituents (metals, metal compounds, non-metal inorganic compounds etc.). For each of these constituents, the fate and hazard profile is used for deriving the proper classification of the UVCB (using the mixture rules) and/or for the derivation of the PNECs of the constituent (forwarded to the risk assessment). Using the fate of all individual constituents circumvents indirectly the issue of varying composition of an UVCB as it implicitly assumes that each time the UVCB substance consists of the pure substance, i.e. that each constituent would be present and bio-available at a 100% concentration in the UVCB substance. This can be considered a conservative approach. A main outcome of the constituents’ based assessment is the selection of all the constituents for which any environmental hazard is identified. This selection defines the scope of the further exposure and risk assessment (CSR, Ch. 9&10).


The actual hazard profile and environmental fate properties of the inorganic UVCB substance and the individual constituents are dependent on the speciation of each and every constituent andhence this information needs to be collected and the correspondinginformation for the environmental fate properties will be used. Different scenarios can be encountered.

·      When the speciation of a constituent is known, this is used as such for the environmental fate properties assessment.

·      When the speciation is unknown or few metal species co-exist, the worst-case speciation for the purpose of environmental fate assessment and environmental hazard assessment is selected, i.e. the speciation that would lead to the most severe effects.


Introduction to environmental fate and pathways

The UVCB is a complex inorganic metals containing substance. The physico-chemical characterization of the UVCB (see relevant section in IUCLID) demonstrates the presence of mainly metallic species. Some streams are massive while others remain in the molten statethrough its whole life cycle (with the exception of routine process sampling). The material has arelatively low solubilisation potential in water for most of the metals present in the UVCB. More particularly the following needs to be taken into account when considering information on environmental fate of this UCVB:

Stability and bio degradation: The classic standard testing protocols on hydrolysis, photo-transformation and biodegradation are not applicable to inorganic substances such as this UVCB. 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 may be possible to incorporate this approach into classification.

As outlined in CLP guidance (2009), understanding of the rate and extent of transformation/dissolution of sparingly soluble inorganic substances to soluble, potentially available metal species is relevant to the environmental hazard assessment.

Attenuation of the released metal ions: once released from the UVCB, the metal-ions will be sorbed to mineral and particulate organic matter surfaces in the water, sediment and soil and will bind to the dissolved organic and sulphide materials present in water, soil and sediment compartments. Binding, precipitation and partitioning allows for a reduction of "bio-available metal species" and thus potential metal toxicity as a function of time.

Transport and distribution: assessing transport and distribution of the UVCB substance has no meaning. The mechanisms of distribution over liquid/solid phase (adsorption/desorption, precipitation and removal from water column) of the metals contained in the UVCB have been assessed in the respective risk assessments and/or Chemical Safety reports. Partition coefficients for soil/water, sediment/water and suspended matter/water are available for different metals contained in the UVCB and further used for environmental exposure assessment, if relevant.

Bioaccumulation and secondary poisoning: the assessment of the bio accumulation and secondary poisoning potential of this UVCB as no meaning. Accumulation data (BCF and BAF values) are available for relevant metal constituents of this UVCB. Metals like Cu, Zn for example are essential and well regulated in all living organisms and therefore the bioaccumulation criterion is not applicable. While some metals do not magnify in aquatic and terrestrial systems, for other metals secondary poisoning is to be considered relevant based on their known bioaccumulation potential.

According to the CLP Guidance for complex substances (section III 3.2) it is not recommended to estimate an average or weighted BCF value but identify one or more constituents for further consideration. Therefore, secondary poisoning of some constituents contained in the UVCB was further taken into account in the environmental exposure assessment.


Summary of the information on environmental fate and pathways for the purpose of classification:

The UVCB environmental hazard assessment fate and pathway of the UVCB is driven by the hazard assessment characteristics of the individual UVCB constituents. For the purpose of the hazard assessment, the fate and pathway of the UVCB is treated as a complex metal containing substance and therefore assessed from the fate and pathways of the discrete constituting compounds (metals, metal compounds, non-metal inorganic compounds). The hazard classifications of each compound are then factored into a combined classification of the UVCB as a whole. For environmental endpoints, additivity and/or summation algorithms are applied to quantitatively estimate the mixture’s toxicity to aquatic organisms. More information can be found in the MECLAS output (see Annex I of the CSR).

The most important fate properties relevant to environmental classification are the limited solubility, assessed from transformation/dissolution tests and attenuation of the released metal ions, assessed as “removal from the water column”. Since the removal from the water column behaviour of the individual constituents can have an indirect impact on their respective environmental classification, an overview is given in the table below.


Table:Summary of the information on environmental fate and pathways for the purpose ofclassification

UVCB constituent

Attenuation/ removal from water column


Speciation* taken forward for Tier 2 environmental classification



Elemental ion

No,see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)


Elemental ion

Yes,see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)


Elemental ion

Yes,see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)


Elemental ion

Yes, see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)


Elemental ion

Yes, see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)


Elemental ion

Yes, see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)


Elemental ion

Yes, see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)


Elemental ion

Yes, see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)

Minors: As, Ni

Elemental ion

In case (worst-case) speciation is classified, see Waeterschoot et al (2012) and MECLAS (Annex I of this CSR)

* see IUCLID/CSR section 1.2 composition and IUCLID 4.23 additional Physico-chemical Information

Summary of the information on environmental fate and pathways for the purpose of risk assessment:

The environmental (risk) assessment is based on measured releases of relevant elements to air and receiving waters for all constituents of the UVCB that are hazardous to the environment. For the environment, most often, it is the metal ion that is the toxic driver (ECHA, 2008, R.7.13-2). Considering the composition and physico-chemical characterisation of this UVCB, only partial release and solubilisation of the various constituting species should be assumed in the aquatic environment. Assuming 100% solubilization into metal ion is therefore conservative as aquatic toxicity is driven by the metal ion.

When quantitative exposure and risk assessment were conducted on a metal constituent, the environmental fate information on this individual metal is reported in the respective IUCLID endpoint summary sheet. The information is taken from the respective metal REACH IUCLID dossiers (see Annex II of this CSR) or the ECHA dissemination website and is summarized in the table below.


Table19:Overview of solid water partition coefficients (Kd), bioaccumulation factors and the fraction of emission directed to water by STP.








Suspended matter (freshwater)







Suspended matter (marine)







Sediment (freshwater)














BCF/BAF (aquatic)







BCF/BAF (terrestrial)

kg/kg dw






Removal rate STP to sludge







*The fraction of Arsenic removed by a biological STP was calculated by means of EUSES 2.1.