Ke. Giller et al., TOXICITY OF HEAVY-METALS TO MICROORGANISMS AND MICROBIAL PROCESSES INAGRICULTURAL SOILS - A REVIEW, Soil biology & biochemistry, 30(10-11), 1998, pp. 1389-1414
An increasing body of evidence suggests that microorganisms are far mo
re sensitive to heavy metal stress than soil animals or plants growing
on the same soils. Not surprisingly, most studies of heavy metal toxi
city to soil microorganisms have concentrated on effects where loss of
microbial Function can be observed and yet such studies may mask unde
rlying effects on biodiversify within microbial populations and commun
ities. The types of evidence which are available for determining criti
cal metal concentrations or loadings for microbial processes and popul
ations in agricultural soil are assessed, particularly in relation to
the agricultural use of sewage sludge. Much of the confusion in derivi
ng critical toxic concentrations of heavy metals in soils arises from
comparison of experimental results based on short-term laboratory ecot
oxicological studies with results from monitoring of longterm exposure
s of microbial populations to heavy metals in field experiments. The l
aboratory studies in effect measure responses to immediate, acute toxi
city (disturbance) whereas the monitoring of field experiments measure
s responses to long-term chronic toxicity (stress) which accumulates g
radually. Laboratory ecotoxicological studies are the most easily cond
ucted and by far the most numerous, but are difficult to extrapolate m
eaningfully to toxic effects likely to occur in the field. Using evide
nce primarily derived from long-term field experiments, a hypothesis i
s formulated to explain how microorganisms may become affected by grad
ually increasing soil metal concentrations and this is discussed in re
lation to defining ''safe'' or ''critical'' soil metal loadings for so
il protection. (C) 1998 Elsevier Science Ltd. All rights reserved.