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Environmental fate & pathways

Bioaccumulation: terrestrial

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Description of key information

A peer-reviewed study (Princz et al, 2014) comparing laboratory-bioaccumulation in earthworms with in silico modelling predictions is available and presented as a key study. This shows no significant bioaccumulation for the test substance in the terrestrial species Eisenia Andrei.
Three papers, Kelly & Gobas, 2003; Kelly et al, 2007; and Gobas et al, 2003, demonstrate that, based on theoretical QSAR modelling, biomagnification may occur in terrestrial food chains. However, these papers are not supported by data on the test substance in question, and therefore remain a theory based on modelling numbers and general trends across similar substances.
A further detailed literature review adds a number of additional data sources, however the literature shows conflicting results. Some studies demonstrate a calculated BCF in excess of 5000, which would result in classification of the test substance as B and vB under the PBT assessment criteria. The models used to calculate these BCFs are criticized in a paper, which claims the models show a number of inaccurate results and classification of chemicals as B and vB may be inaccurate when used.
Ultimately, the Princz paper, which includes solid, validated laboratory data, provides the most useful and reliable information on the test substance. This shows that bioaccumulation does not occur in terrestrial species. The papers by Kelly & Gobas, 2003, Kelly et al, 2007, and Gobas et al, 2003, suggest biomagnification, but this is not supported by the Princz data which shows that bioaccumulation will not occur in terrestrial soil organisms and therefore making it unlikely that the substance would enter the food chain.

Key value for chemical safety assessment

Additional information

A single study (Princz et al, 2014), Klimisch score of 1, is presented as a key study. This has been conducted to OECD guideline 317 guidelines and also includes comparison within silicodata, and the results show no significant bioaccumulation of the test item in the earthworm speciesEisenia Andrei. The study results were comparable to thein silicomodelling, and resulted in a BSAF of 0.13 – 0.32 g organic carbon/g lipid in a clay soil and 0.067 – 3.5 g organic carbon/g lipid in a sandy soil.

 

Papers were also highlighted by ECHA in their draft decision of May 6th, 2015), including Kelly & Gobas (2003); Kelly et al (2007); and Gobas et al (2003). An overview of the data is presented below.

 

These three literature sources usein-silicomethods in conjunction with select field studies to study the potential bioaccumulation of Persistent Organic Pollutants (POPs). The specific test material in question was not included. The papers all provide similar conclusions on potential bioaccumulation of POPs.POPs with an octanol-water partition coefficient, logKOW, in excess 2 and an octanol-air partition coefficient, logKOA,­ in excess of 5 show potential for bioaccumulation in terrestrial food chains. Based on this criteria, TBMD could be considered bioaccumulative, as it has a measured logKOWof >6.5 and a calculated logKOA­­value of 17.015. This conclusion is purely speculative, as no measured data for the target substance is provided within the studies. As detailed in the key study byPrincz et al, 2014, measuredin vivodata showed that bioaccumulation in a terrestrial earthworm species does not occur. As such, the data provided in these three papers by Kelly and Gobas are considered only supplementary and of lesser dependability that actual measuredin vivodata. These studies are therefore not considered as key studies for the submission.

 

There are four additional studies which predict the bioconcentration factor for substances using a variety of methods. Tyle et al (2002) have identified a number of PBT and vPvB substances using QSAR technology which shows that it has a calculated BCF of 5623 using the Connell calculation approach, which classifies the substance as both B and vB. A PHD dissertation by Inoue (2012) further supports the high BCF value for the target substance, showing a 5% lipid normalized BCF of 8100. This dissertation also suggests that biomagnification would occur in the food chain, supporting the findings of the three above referenced Kelly and Gobas studies.

 

However, a further QSAR study on bioaccumulation potential undertaken by Dimitrov et al (2003) offers conflicting results, discrediting the Connell, Meylan and Dimitrov models as they show a number of incorrect B and vB classifications, thereby making them inadequate for legislative purposes. Ultimately, it suggests that the target substance is not classified as B or vB, but only P, given the classification in the CATABOL and BCFMAX­models.

 

There is a disparity within the literature available as to the actual BCF value of the target substance, 2,2’,6,6’-tetra-tert-butyl-4,4’-methylenediphenol, and whether this substance should be classified as B, vB or not at all. The Princz et al study (2014)shows that no bioaccumulation occurs in earthworms. As this is the only available formal study data on the test material, with other papers either using a QSAR model on the test substance or its analogues and therefore only operating in a theoretical sphere, it is believed that the results of the Princz study should be taken as the most pertinent and reliable results.

 

Reference list:

 

Tyle, H. et al (2002), Identification of potential PBTs and vPvBs by use of QSARs,Danish EPA summary report

Dimitrov, S.D. et al (2003), Bioconcentration potential predictions based on molecular attributes—an early warning approach for chemicals found in humans, birds, fish and wildlife,QSAR Comb. Sci. 22

Gobas, F.A.P.C. et al (2003), Quantitative Structure Activity Relationships for Predicting the Bioaccumulation of POPs in Terrestrial Food-Webs,QSAR Comb Sci, 22:329-336.

Inoue, Y. (2012), Studies on an evaluation method for bioaccumulation of chemicals in fish,Kyushu University, Japan, February 2012

Kelly, B.C. et al (2007), Food Web-Specific Biomagnification of Persistent Organic Pollutants,Science 317:236-239

Kelly, B.C. and Gobas, F.A.P.C. (2003), An Arctic Terrestrial Food-Chain Bioaccumulation Model for Persistent Organic Pollutants,Environ Sci Technol, 37:2966-2974