Bioaccumulative substance

PBTs (in addition to those listed by governmental organizations) vPvBs (very persistent, very bioaccumulating) substances... 

Persistent, Bioaccumulative and Toxic and Very Persistent and Very Bioaccumulative Substances... 

Also bioaccumulating substances may in some situations call for a higher assessment factor. If accumulation is likely, the toxicity studies need to be of sufficient length to cover the accumulation period (e.g., the time to reach a steady-state concentration). If there is limited information on these aspects, it has to be considered to which extent this lack of information should affect the assessment factor. 

The Binational Toxics Strategy between the USA and Canada has identified 12 bioaccumulative substances (referred to as Level-1 substances) having significant persistency and toxicity to the Great Lakes system, with the goal of reducing the sources of these substances to achieve naturally occurring levels [23]. Six of the 12 Level-1 substances are OC pesticides aldrin/dieldrin, chlordane, DDT, HCB, mirex, and toxaphene. Several other OC pesticides, such as endrin, heptachlor/heptachlor epoxide, hexachloro-cyclohexanes, tetra- and penta-chlorobenzenes, and pentachlorophenol, have been identified as Level-2 substances. 

Bioaccumulants Substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted. (See Biological magnification.)... 

For ecological receptors, a similar approach may be employed for secondary receptors that could be influenced by a change in the soil environment. For instance, it is possible to model the potential for soil to influence an adjacent surface water body and therefore to screen the soil criteria for impacts on an aquatic receptor. When applied, this leads to intercompartment harmonization of standards, by which soil or sediment standards pose no problems for water bodies and vice versa. In addition, it may be possible to use screening-level models to assess the potential for a bioaccumulable substance to influence a tertiary ecological receptor, usually a top predator or a protected species. In this approach, the reference dose can be borrowed from other sources (e.g., use of an aquatic criterion to determine a critical water concentration). The model is then used only to assess how the soil may influence transfer to the critical receptor. However, it should be noted that this type of procedure cannot be used for guideline development related to primary terrestrial receptors since there are no reliable models to estimate dose-response relationships for these receptors. Therefore, other techniques described in this chapter are recommended for screening against primary receptors. 

Concerns about using data from sub-chronic toxicity tests (30 and 90-day studies, respectively) for bioaccumulating substances are described as a source of uncertainty in the Penta and the Octa documents. 

The uncertainties identified in connection with these conclusions include questions about the adequacy of the method used to calculate a MOS for bioaccumulative substances like Octa, as well as a similar methodological uncertainty linked to the current PEC/PNEC approach for secondary poisoning in terms of both the PEC and the PNEC (which could lead to an underestimation of risk). The risk assessment report also identifies a general uncertainty connected with the strength of the scientific basis for drawing conclusions on the current and future environmental risks of Octa. 

The Octa and Deca risk assessors also indicate the need to develop more suitable methods for risk assessment of bioaccumulating substances. 

Figure 3.6 The tetra and penta congeners of PBDEs, which are strongly bioaccumulating substances.

Measurement in biota is relevant for the most bioaccumulative substances. Concentrations in biota can vary depending among other things on biological factors such as the species, age, fat content, sex, etc. To reduce variability due to these factors and allow data comparison it is important to measure the most significant ones (factors) and normalise the concentrations against them before data can be assessed. 

SCCPs are persistent and bioaccumulative, and thus concentrations in the environment and biota are expected to increase with continued release to the environment. Standard risk assessment methods comparing effect levels to environmental concentrations may underestimate the risk of persistent and bioaccumulative substances, such as SCCPs. Persistent substances can take decades to reach a maximum steady state concentration in the environment, resulting in an underestimation of the potential exposure to these compounds if steady-state has not been achieved, and releases into the environment continue. Similarly, it can take a long time for persistent and bioaccumulative substances to reach a maximum steady-state concentration within an organism this is supported by the observations of Sochova et al., [62] who noted an increase in toxicity of SCCPs for longer exposure duration with nematodes. The durations of standard toxicity tests may be insufficient to achieve the maximum tissue concentration, resulting in an underestimation of the effect threshold. 

Screening toxicity tests are conducted on a non-biodegradable but non-bioaccumulative substance. These are a 28-d subacute oral toxicity study, an Ames test and an in vitro chromosome aberration test in cell lines. The 28-d subacute toxicity study must include a satellite group (dosed at the maximum level of the main study) with a... 

Where a substance is persistent, bioaccumulative and toxic (PBT) or very persistent and very bioaccumulative (vPvB) in accordance with the criteria set out in Annex XIII criteria for the identification of persistent, bioaccumulative and toxic substances, and very persistent and very bioaccumulative substances of REACH legislation or... 

The bioaccumulation of a substance into an organism is not an adverse effect hazard in itself. Bioconcentration and bioaccumulation may lead to an increase in body burden which may cause toxic effects due to direct and/or indirect exposure. Bioaccumulative substances characterized by high persistence and toxicity, negligible metabolism and a log ATow between 5 and 8 may represent a concern when widely dispersed in the environment. The potential of a substance to bioaccumulate is primarily related to its lipophilicity. A surrogate measure of this quality is the n-octanol - water partition coefficient (/fow), which is correlated with bioconcentration potential. Therefore, /fow values are normally used as predictors in quantitative structure - activity relationships (QSARs) for bioconcentration factors (BCFs) of organic non-polar substances. 

Bioaccumulative substances that concentrate in living organisms as they breathe contaminated air, drink or live in contaminated water, or eat contaminated food rather than being eliminated through natural processes. 

Criteria for the Identification of Persistent, Bioaccumulative, and Toxic Substances (PBT substances) and Very Persistent and Very Bioaccumulative Substances (vPvB substances)... 

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