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PBT assessment

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PBT assessment: overall result

PBT status:
PBT assessment does not apply

The PBT and vPvB criteria of Annex XIII to the Regulation does not apply to inorganic substances.The assessment approach for Persistent, Bioaccumulative, and Toxic (PBT) substances was established because of the possibility that some man-made chemicals may accumulate in parts of the environment, and whereby such an accumulation may cause unpredictable effects in the long term that may be very difficult to reverse.


These PBT criteria are not directly applicable to metals as it neglects various processes affecting the fate, bioavailability and toxicity of inorganic compounds. (partitioning, speciation, complexation, competition with other ions, adsorption, precipitation, dissolution etc.). A unit world model (UWM) was proposed as an alternative to the PBT criteria and has the potential to be used for the hazard assessment of both metal ions and organic chemicals. The primary advantage of the UWM approach for hazard assessment is that it goes beyond the individual consideration of persistence, bioaccumulation, and inherent toxicity by integrating them to give an overall expression of hazard in the form of a critical loading. In doing so, it circumvents the problem of the inherently infinite persistence of metals and, potentially, provides a consistent and more level playing field for assessing these diverse substances (Harvey et al., 2007). The UWM can also take into account the effect of speciation and water properties (pH, hardness etc.) on bioavailability and toxicity. 


8.1.1      Persistence Assessment

Metals are obviously persistent in the sense that they do not degrade to CO2, water, and other elements of less environmental concern. As a consequence, it has been argued that traditional persistence measures used for organic substances do not equally apply to metals (Adams et al. 2000). While it is recognized that metals are conserved, the form and availability of the metal can change and the persistence of the bioavailable species is the more appropriate hazard indicator for metals.


This potential transformation of metal species to non-bioavailable forms through complexation, precipitation, adsorption, and settling is recognized in Annex IV of Guidance to Regulation (EC) No 1272/2008 on Classification, Labelling and Packaging of substances and mixtures. For soluble metal species, a rapid removal definition based on laboratory, mesocosm, and/or field data tests has been proposed. The term “Rapid removal” is a more accurate description for metals in this respect, because, partitioning (e.g. by precipitation and especially speciation processes) can lead to the non-available form and the elimination of metals from the water column. However, caution is advised given the possibility that 1) these processes do not necessarily reduce bioavailability and/or 2) the reduction in bioavailability afforded by these processes is not necessarily permanent. In accordance with the principles of rapid removal used for organic substances rapid removal can be defined for metals as a reduction of the soluble metal species by > 70% in 28 days.


A preliminary assessment on the removal of Pb from a water column based on the standard lake as defined in EUSES model (suspended solids: 15 mg/L; depth: 3 m; settling rate: 2.5 m/d and residence time 40 days) and a constant partition coefficient for Sb to suspended matter (log Kp = 5.47 l/kg) is shown in the Figure attached (Total and dissolved Pb removal from the water column using EUSES standard lake parameters and a constant log Kp of 5.47 l/kg).


This assessment does not take into account potential remobilisation due to e.g. resuspension or diffusion. Based on a log Kp of 5.47 l/kg, it is predicted that 82% of the Pb added to the water column (initial total Pb concentration of 0,1 mg/l) is adsorbed on the suspended matter. Therefore, the initial partitioning of Pb to suspended solids immediately satisfies the 70% removal requirement.


Similar results are obtained for speciation model-calculated (using WHAM) distribution coefficients (Kp), i.e. lead removal from the water column of a generalized lake based upon the EUSES model lake exceeds 70% removal in 28 days. Sensitivity calculations indicate 70% removal in 28 days can be achieved at water column depths exceeding the EUSES lake value (3 m) by factors of 15 or greater. Further sensitivity calculations also indicate that 70% removal is still achieved within 28 days when the settling velocity is decreased from 2.5 m/d to 0.24 m/d which is the low end of the POC range. Finally, the potential for remobilization from anoxic and oxic sediments, quantified by comparing water column lead concentrations resulting from sediment feedback to the 70% removal concentration, is 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.


In conclusion, the criterion for persistence based on degradation is not applicable for inorganic Pb. Under conditions of a standard EUSES lake and different estimated partition coefficient for suspended matter, Pb meets the criteria for rapid removal from the water column.

8.1.2       Bioaccumulation Assessment

Bioaccumulation is the process whereby aquatic organisms accumulate substances in their tissues from water and diet. Bioaccumulation is of potential concern both because of the possibility of chronic toxicity to the organisms accumulating substances in their tissues and because of the possibility of toxicity to predators eating those organisms. Some metal-specific considerations need to be made on the concept of bioaccumulation. Due to their natural occurrence, biota will naturally accumulate metals at least to some degree without deleterious effect (ICMM, 2007). For most metals and inorganic metal compounds the relationship between water concentration and BCF in aquatic organisms is inverse, and bioconcentration data are therefore often not reliable predictors of chronic toxicity or food chain accumulation in the aquatic environment. Unlike organic substances, which may be taken up by passive diffusion across cell walls, the uptake and removal processes of essential elements are actively regulated in order to maintain a reasonable constant internal concentration (homeostatis). Also non-essential metals such as Pb are homeostatically regulated to some extent and therefore also for non-essential metals, an inverse relationship between the metal concentration and the external concentration may be observed (McGeer et al., 2003). 


According to the REACH guidance R7c (2012) ‘the observed variability in bioaccumulation and bioconcentration data due to speciation and especially homeostatic regulation can therefore complicate the evaluation of data (Adams & Chapman, 2006). The data may be used for assessments of secondary poisoning and human dietary exposure. However, special guidance is required for classification of metals and inorganic substances are currently outside the scope of PBT assessments’.


Moreover, according to the REACH guidance R11 on PBT assessment (2012) 'the PBT and vPvB criteria of Annex XIII to the Regulation do not apply to inorganic substances but shall apply to organo-metals'.


In conclusion, the ‘bioaccumulative’ criterion is not applicable to Pb.


8.1.3       Toxicity Assessment

A substance is considered to fulfil the toxicity criteria (T) when the long-term no-observed effect concentration (NOEC) / EC10for marine or freshwater organisms is less than 10μg/L or when it is classified as carcinogenic (category 1A or 1B), germ cell mutagenic (category 1A or 1B), or toxic for reproduction (category 1A, 1B or 2) or there is evidence of chronic toxicity (STOT RE 1 or STOT RE 2) according to the CLP Regulation.



The long term NOEC/EC10forfreshwaterorganisms are situated between 0.48* μg Pb/L (L. stagnalis, 7 days, reproduction; pH: 6.9, DOC: 3.96 mg/L; H: 87.0 mg/l CaCO3) and 1558.6μg Pb/L (P. promelas, 7 days, dry weight; pH: 7.35, DOC: 6.95 mg/L; H: 60 mg/l CaCO3). In total, 180 NOEC/EC10values are available for 27 different freshwater species, of which 25 NOEC/EC10values are lower than 10μg/L. The normalised freshwater HC5,50%under worst-case conditions (DOC 2.6 mg/L; pH 6.6) is 4.7μg Pb/L. The PNECfreshwater is 2.4μg Pb/L.


*NB extrapolated value

The long term NOEC/EC10 for marine organisms are situated between 9μg Pb/L (M. trossulus, 48 hours, abnormalities) and 1409.6μg Pb/L (M. galloprovincialis, 48 hours, mortality). In total, 59 NOEC/EC10values are available for 20 different marine species, of which 4 NOEC/EC10values are lower than 10μg/L. The normalised marine HC5,50%under worst-case conditions (DOC 1.2 mg/L; pH 8.1) is 6.5μg Pb/L. The PNECmarineis 3.3μg Pb/L.


In conclusion, Pb fulfil the toxicity criteria based on the most sensitive NOEC, HC5-50 and PNEC values, which are below 10μg/L.


8.1.4          Summary and overall Conclusions on PBT or vPvB Properties

- The criterion for ‘persistence’ is not applicable for inorganic Pb. Under conditions of a standard EUSES lake and different estimated partition coefficient for suspended matter, Pb meets the criteria for rapid removal from the water column (> 70% in 28 days). 

- The criterion for ‘bioaccumulation’ criterion is not applicable to inorganic substances such as Pb.

- Pb is considered to be toxic, since the most sensitive NOECs, HC5-50 and PNEC values are lower than 10μg Pb/L.