Earthworms in Environmental Research - Earthworm Ecology - page 320

E prey
E lab. food

EMR total bird
EMR species concern

------------------------------------------- * FMR norm. condition
FMR peak activity

NOEC prey = NOEC lab. food * --------------------* -------------------------------------------

where E is the energy content, FMR is the field metabolic rate, EMR is the existence metabolic
rate, and BMR is the basal metabolic rate.
These last three models all assume a stochastic response for exposure of earthworms to
chemicals and thus introduce probability into the risk estimates derived. The third step in these
model developments introduces earthworm population dynamic elements. A major problem is the
need to validate the model parameters by field data. Ma and Van der Voet (1993) proposed a
nonlinear, age-dependent relationship for the predators, in combination with the BCF earthworm and
the bioavailable fraction of the chemical in the soil and theoretically derived chemical uptake rates
for the various organs of the predators. It was possible in this way to predict target organ contaminant
loads as functions of ingestion of the contaminant, its assimilation rate, and internal partitioning
in the earthworm.
A fourth step is to integrate these uptake mechanisms into ecosystem processes such as the
cycling of biomass through an ecosystem. Effectively, it is the cycling of biomass that steers the
accumulation rate of a contaminant through trophic levels in the food chain. This approach is used
in the CATS model, which analyzes the cadmium cycle in a meadow ecosystem based on the C
and N cycles and the resulting biomass transfers between the different pools in the system (Traas
and Aldenberg 1992).
These results and estimates can be expressed in different ways. They can be expressed as the
relationship between potential environmental concentration (PEC) and the no effect concentration
(NEC), the PEC/NEC ratio (Romijn et al. 1991; Luttik et al. 1993; Noppert et al. 1994). Using
this, uptake of diazinon by earthworms can be described as a risk for passerine birds because of
the sensitivity of these birds to this pesticide (Stephenson et al. 1997). But, it is also possible to
define a potential risk area around a point pollution source (Gorree and Tamis 1992) or an exposure
risk criteria for target organs (Ma and Van der Voet 1993).
In all food chain contaminant uptake studies, the role of earthworms, or soil invertebrates in
general, as the intermediary between soil and terrestrial predators proved crucial. BCFs for soil
earthworms, in all cases, had the highest levels, as exemplified by Ma (1994) (Table 17.3). Because
of their high bioaccumulation potential and relatively low sensitivity to certain toxic compounds,

earthworms are major toxicity sources for many terrestrial predators ( Table 17.4 ) , as shown con-

vincingly in the extensive model studies of Klok (2000).

TABLE 17.3
Concentration Factors (CFs) for
Cadmium and Lead in Herbivore
and Decomposer-Based
Terrestrial Food Chains

Species Group CF cadmium CF lead

Coleoptera 1.3Ï6.5 0.2Ï0.5

Carabidae 1.5Ï9.5 0.09Ï0.3

Aranea 18Ï86 0.3Ï0.5

Opiliones 5.5Ï23 0.1Ï0.8

Lumbricidae 32Ï136 1.3Ï3.0

Grass 0.5Ï2.5 0.07Ï0.3

Soil (mg kg −1 ) 0.2Ï2.9 20Ï130