Earthworms can therefore be considered as a terrestrial organism of choice in risk
assessment for identifying sources of pollution or to better understanding the input of
contaminants in food chains. Concerning the environmental fate and behaviour of
chemicals, the Organisation for Economic Co-operation and Development (OECD)
proposed guidelines to assess the bioaccumulation of chemicals in soil oligochaetes
Test No. 317 [104]. Recommended test species in this guideline include Eisenia
fetida and Eisenia andrei (Lumbricidae), or white worms Enchytraeus albidus,
Enchytraeus crypticus or Enchytraeus luxuriosus (Enchytraeidae). The test consists
of two phases: an uptake phase, where test organisms are exposed to the test
substance incorporated directly into the soil, and an elimination (post-exposure)
phase. Following analysis, parameters which characterise the bioaccumulation of a
chemical substance can be determined including the bioaccumulation factor (BAF),
the uptake rate constant and the elimination rate constant.
Based on the recommendations outlined in the OECD guideline, the kinetics of
pharmaceutical uptake in earthworms were evaluated by Carter et al. [105] in a series
of radiolabelled laboratory experiments. Variability in pharmaceutical accumulation
between chemicals was observed, with calculated pore water-based bioconcentration
factors (BCFs) increasing in the order of carbamazepine < diclofenac < fluoxetine
< orlistat. The relatively large BCF of 51.5 for orlistat was suggested to be
attributable to the minimal elimination of this chemical in the depuration phase,
whereas for carbamazepine, the fast elimination rate of 0.14 d
À1 could account for
the smaller BCF of 2.21. Differences in key physiochemical properties known to
control the fate of chemicals, such as hydrophobicity, were also suggested to be
responsible for the observed differences in accumulation between chemicals. For
example, BCFs increased in a similar order to the increase in octanol-water partition
coefficients (log K ow ) for the respective compounds, supporting previous research
that has suggested that the degree of hydrophobicity has a key role to play in the
uptake of pharmaceuticals into organisms. However, unlike neutral organic compounds, the uptake of ionisable pharmaceuticals was found to not be driven solely by
the hydrophobicity of the chemical.
It has been widely published in scientific literature that pharmaceuticals can
behave very differently in different soil types [106]. For example, distribution
coefficients (K d ) between soil particles and soil pore waters are known to vary by
several orders of magnitude for a range of pharmaceuticals in soils with varying
properties [107]. Such differences in pharmaceutical fate would strongly influence
the bioavailable fraction of pharmaceuticals available for uptake by soil dwelling
species, and indeed, differences in uptake between soil types were observed by
Carter et al. [108] in a later study assessing uptake of four chemically distinct
pharmaceuticals in five soil types. BCFs of the individual compounds were found
to differ across soil types, with greatest variability observed for diclofenac
(7.02–69.57) and orlistat (30.50–115.88), whereas smaller variability of the BCFs
was noted for fluoxetine (14.09–20.42) and carbamazepine (1.05–1.61). However,
further analysis by Carter et al. [108] to understand the relationship between soil and
pore water properties and earthworm uptake failed to highlight any key parameters
which may be responsible for pharmaceutical uptake into earthworms. Ultimately,
Uptake and Effects of Pharmaceuticals in the Soil-Plant-Earthworm System
203
assessment for identifying sources of pollution or to better understanding the input of
contaminants in food chains. Concerning the environmental fate and behaviour of
chemicals, the Organisation for Economic Co-operation and Development (OECD)
proposed guidelines to assess the bioaccumulation of chemicals in soil oligochaetes
Test No. 317 [104]. Recommended test species in this guideline include Eisenia
fetida and Eisenia andrei (Lumbricidae), or white worms Enchytraeus albidus,
Enchytraeus crypticus or Enchytraeus luxuriosus (Enchytraeidae). The test consists
of two phases: an uptake phase, where test organisms are exposed to the test
substance incorporated directly into the soil, and an elimination (post-exposure)
phase. Following analysis, parameters which characterise the bioaccumulation of a
chemical substance can be determined including the bioaccumulation factor (BAF),
the uptake rate constant and the elimination rate constant.
Based on the recommendations outlined in the OECD guideline, the kinetics of
pharmaceutical uptake in earthworms were evaluated by Carter et al. [105] in a series
of radiolabelled laboratory experiments. Variability in pharmaceutical accumulation
between chemicals was observed, with calculated pore water-based bioconcentration
factors (BCFs) increasing in the order of carbamazepine < diclofenac < fluoxetine
< orlistat. The relatively large BCF of 51.5 for orlistat was suggested to be
attributable to the minimal elimination of this chemical in the depuration phase,
whereas for carbamazepine, the fast elimination rate of 0.14 d
À1 could account for
the smaller BCF of 2.21. Differences in key physiochemical properties known to
control the fate of chemicals, such as hydrophobicity, were also suggested to be
responsible for the observed differences in accumulation between chemicals. For
example, BCFs increased in a similar order to the increase in octanol-water partition
coefficients (log K ow ) for the respective compounds, supporting previous research
that has suggested that the degree of hydrophobicity has a key role to play in the
uptake of pharmaceuticals into organisms. However, unlike neutral organic compounds, the uptake of ionisable pharmaceuticals was found to not be driven solely by
the hydrophobicity of the chemical.
It has been widely published in scientific literature that pharmaceuticals can
behave very differently in different soil types [106]. For example, distribution
coefficients (K d ) between soil particles and soil pore waters are known to vary by
several orders of magnitude for a range of pharmaceuticals in soils with varying
properties [107]. Such differences in pharmaceutical fate would strongly influence
the bioavailable fraction of pharmaceuticals available for uptake by soil dwelling
species, and indeed, differences in uptake between soil types were observed by
Carter et al. [108] in a later study assessing uptake of four chemically distinct
pharmaceuticals in five soil types. BCFs of the individual compounds were found
to differ across soil types, with greatest variability observed for diclofenac
(7.02–69.57) and orlistat (30.50–115.88), whereas smaller variability of the BCFs
was noted for fluoxetine (14.09–20.42) and carbamazepine (1.05–1.61). However,
further analysis by Carter et al. [108] to understand the relationship between soil and
pore water properties and earthworm uptake failed to highlight any key parameters
which may be responsible for pharmaceutical uptake into earthworms. Ultimately,
Uptake and Effects of Pharmaceuticals in the Soil-Plant-Earthworm System
203