Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

in an oak woodland site 3 km from a Pb-Zn smelter in Bristol, England, compared to a reference
site 23 km from the smelter. The differences were most dramatic when expressed per unit mass
of litter. Several species that were abundant in the reference site were not found in the
contaminated woodland. For example, the abundance of the woodlice Trichoniscus pusillus
was 151 individuals per m 2 in the reference woodland, but none were found in the contaminated
soils. This was also true of 2 of the 3 millipede species, and 4 of the 5 earthworm species
studied. At six sites within 1 km from the smelters, no earthworms were present at all (Spurgeon
and Hopkin, 1996a). Contamination at this site has apparently reduced both the population and
biodiversity of the soil invertebrate community.
The effect of metal pollution on soil invertebrates may be a threshold-type response. In a
study conducted in woodlands near two zinc smelters in Noyelles-Godault, in northern France,
soils at the most polluted site were devoid of mites and millipedes, while the remaining sites had
diversity measures similar to control sites (Grelle et al., 2000).
While Pb pollution affects the population and diversity of soil fauna, there is little
evidence of significant bioaccumulation of Pb in the soil food web (see also Section AX7.1.3).
In the Bristol, England study, Pb concentrations in earthworms were lower than soil Pb
concentrations and much lower than litter Pb concentrations (Martin and Bullock, 1994). Litterdwelling
mites had Pb concentrations that were 10% of the average litter concentration. The
predator centipedes Lithobius forficatus and L. variegatus had mean Pb concentrations of
18.6 and 44.0 mg kg !1 , respectively, two orders of magnitude lower than the Pb concentration of
litter (2193 mg kg !1 ) and lower than the concentrations of their known prey species. In a study
conducted in a Norway spruce forest affected primarily by automobile exhaust from a nearby
highway, earthworms had Pb concentrations similar to the soil (Roth, 1993). Almost all of the
litter decomposers, however, had Pb concentrations that were less than 20% of the litter. All but
3 of the zoophagous arthropods had Pb concentrations that were less than 40% of their prey; the
remaining 3 had Pb concentrations similar to their prey. Because of the absence of significant
bioaccumulation in the soil food web, predator species will be affected by Pb pollution primarily
through effects on the abundance of their prey (Spurgeon and Hopkin, 1996b).
Taken as a whole, ecosystem-level studies of the soil food web indicate that Pb can affect
energy flows in terrestrial ecosystems through two principal mechanisms. In the most severely
polluted sites, the death of primary producers directly decreases the flow of energy into the
AX7-102