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Environmental fate & pathways

Bioaccumulation: terrestrial

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Description of key information

Comparable statistics for bioaccumulation in plants, earthworms and small mammals, i.e. a multi-species BSAF of 0.0375, 0.26 and 0.0038, respectively, indicate that plants, earthworms and small mammals accumulate arsenic to levels much lower than those measured in the associated soils. the BSAF of 0.22 for invertebrates was selected for the chemical safety assessment

Key value for chemical safety assessment

BCF (terrestrial species):
0.22 dimensionless

Additional information

Plants:

A total of 122 BSAF soil-plant values from 27 plant species ranging from 0.00006 to 9,074 (log-normal distribution) were summarized with a median of 0.0375 indicating that above-ground plant tissues in the majority of the assessed studies accumulated arsenic to levels much lower than those measured in the associated soils (Efroymson et al., 2001). The median BSAF soil-plant value of 0.0375 was considered for the chemical safety assessment.

In a study by Martin & cowie (2009), 98 field-measured soil-plant bioaccumulation data points were summarized and allocated to different produce groups. The geometric means of BSAF soil-plant values on a dry weight basis for different produce groups range from 0.0002 to 0.011 indicating that edible parts of plants in all of the assessed studies accumulated arsenic to levels much lower than those measured in the associated soils.

Invertebrates:

A total of 53 BSAF soil-earthworm values ranging from 0.01 to 0.93 (normal distribution) were summarized with a median of 0.22 indicating that earthworms in all of the assessed studies accumulated arsenic to levels much lower than those measured in the associated soils (Sample et al., 1999). The median BSAF soil-earthworm value of 0.22 was selected for the chemical safety assessment.

Small mammals:

A total of 46 BSAF soil-mammal values from 8 species ranging from 0.0003 to 0.0217 (log-normal distribution) were summarized with a median of 0.0038 indicating that small mammals tissue in all of the assessed studies accumulated arsenic to levels much lower than those measured in the associated soils (Sample et al., 1998). The median BSAF soil-mammal value of 0.0038 was considered for the chemical safety assessment.

Summary:

Terrestrial plants may accumulate arsenic by root uptake from the soil or by absorption of airborne arsenic deposited on the leaves, and certain species may accumulate substantial levels. Yet, even when grown on highly polluted soil or soil naturally high in arsenic, the arsenic level taken up by the plants is comparatively low (according to ATSDR, 2007). Comparable statistics for bioaccumulation in plants, earthworms and small mammals, i.e. a multi-species BSAF of 0.0375, 0.26 and 0.0038 indicate that plants, earthworms and small mammals, respectively, accumulate arsenic to levels much lower than those measured in the associated soils (Efroymson et al., 2001; Martin & Cowie, 2009; Sample et al., 1999). BSAF values measured for total above-ground tissues (Efroymson et al., 2001) are higher than BSAF values for specific plant parts as summarised by Martin & Cowie (2009), which may be explained by the fact that only specific plant parts were analysed in the latter study. However, in the context of an environmental risk assessment, BSAF values for specific plant parts may underestimate bioaccumulation as organisms at the higher trophic level may not only consume specific parts.

Regarding the arsenic uptake in terrestrial organisms, earthworms seem to accumulate more than small mammals. Thus, biomagnification of arsenic in terrestrial food chains up to the level of small mammals does not appear to be significant, including herbivores and omnivores (sufficient data are not available for insectivores) as BSAF values were higher at lower trophic levels.

In sum, BSAF values exist for various species of plants, invertebrates and small mammals, and the BSAF of 0.22 for invertebrates was selected for the chemical safety assessment.