Diarsenic trioxide

Bioaccumulation: terrestrial

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Remarks:

Publication has been subject to peer and adminsitrative review. Scientific methodology is in line with ECHA Guidance on information requirements & CSA, Appendix R.7.13-2: Environmental risk assessment for metals and metal compounds (2008).

Qualifier:

no guideline followed

Principles of method if other than guideline:

Computation of BSAF values based on literature data: The selection of field data from journal articles, data processing and computing is in line with ECHA Guidance on information requirements & CSA, Appendix R.7.13-2: Environmental risk assessment for metals and metal compounds (2008).

GLP compliance:

not specified

Radiolabelling:

no

Details on sampling:

Field studies in which soil and resident earthworms are sampled. Only sites at which contamination had been present for at least 1 year, so all earthworm tissue burdens were assumed to be at equilibrium with soil concentrations.
Because soil residues in the earthworm gastrointestinal (GI) tract may be highly variable and therefore may significantly bias body burden measurements, only depurated earthworms were included.

Test organisms (species):

other: earthworm species

Key result

Type:

BSAF

Value:

0.22 dimensionless

Basis:

whole body d.w.

Calculation basis:

steady state

Remarks on result:

other: median of 53 BSAF soil-earthworm values

BAFsoil-earthworm [dw]	Mean	SD	Median	Minimum	Maximum	n
	0.26	0.24	0.22	0.01	0.93	53

Conclusions:

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. The median BSAF soil-earthworm value of 0.22 was selected for the chemical safety assessment.

Description of key information

A compilation of field-based soil-earthworm BSAF values reports 53 BSAF values for As ranging from 0.01 to 0.93, with a median of 0.22 (dry weight based), indicating that earthworms accumulated arsenic to levels lower than those measured in the associated soils (Sample et al., 1999). These findings were confirmed by field based BSAF value for earthworms from 3 more recent studies, reporting 21 BSAF values ranging between 0.02 and 1.75, with a median of 0.21 (Button et al., 2010; Button et al., 2011 and Button et al., 2012). The median BSAF soil-earthworm value of 0.22 was selected for the chemical safety assessment.

Key value for chemical safety assessment

BCF (terrestrial species):

0.22 dimensionless

Additional information

Only field-based bioaccumulation factors based on total As concentrations in organisms and in corresponding soils were selected for the assessment of the bioaccumulation of As in aquatic or soil organisms. This ensures that biota As burdens are in equilibrium with As concentrations in their environment and are exposed via all relevant uptake routes.

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). These findings were confirmed by field based BSAF value for earthworms from 3 more recent studies, reporting 21 BSAF values ranging between 0.02 and 1.75, with a median of 0.21 (Button et al., 2010; Button et al., 2011 and Button et al., 2012). 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, 0.22 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.