The relation between extrapolated risk, expressed as potentially affected fraction, and community effects, expressed as pollution‐induced community tolerance

Abstract

The results of toxicity tests can be used to calculate the potentially affected fraction (PAF) of species in an ecosystem at a given pollutant concentration using statistical extrapolation methods. The PAF curve indicates the fraction of species from the original community that may become inhibited at each elevated pollutant concentration and is a measure of the ecotoxicological risk. Pollution-induced community tolerance (PICT) is a true community response that is measured under controlled conditions in the laboratory, using organisms from contaminated field sites. Microorganisms from experimental field plots with added Zn were exposed to various concentrations of Zn in the laboratory and the mineralization of 14C acetate was monitored. Microorganisms from plots with Zn concentrations above 124 mg/kg showed a significant increase in the effect concentration 10% (EC10) and, therefore, had a significant PICT. The pore-water concentrations of Zn in these field soils were in the same magnitude as the EC10 of the microorganisms from these soils. The PAF curve was calculated from previously reported toxicity tests with five different microbial species using the average and the standard deviation of the logarithmically transformed EC10 values. The average sensitivity of this PAF curve was similar to the EC50 of the acetate mineralization curve from the field plot without added Zn2+, but the PAF curve was less steep. Our experiments indicated that 27 to 84% of the original microbial species were inhibited at Zn concentrations from 334 to 1,858 mg/kg soil, respectively. Our results suggest that the PICT method can now also be used to quantify the fraction of the original species composition that is inhibited at a specific pollutant concentration.

Location‐specific ecotoxicological risk assessment of metal‐polluted soils

“…We realized that metal precipitation in the Biolog plates hindered the straightforward application of PICT in risk assessment. This was much higher than the EC50 of the 14 C acetate mineralization of 1 mg Zn/L measured in Tris buffer [20] of the same control plot. Bistris has a positively charged amine as buffer molecule, which does not interact with positively charged metal ions.…”

“…However, full deployment of this array harbors promising possibilities for PICT as a sensitive method to determine ecological shifts [20,26,30] to be used in risk assessment schemes. This possibility was not fully elaborated in this investigation because the average values did demonstrate a sufficient discriminative strength.…”

“…Pollution-induced community tolerance is observed mostly with compounds with a specific mode of action because these compounds have a wide species-sensitivity distribution [20]. The specificity of the test is both an advantage and a disadvantage because one has to know the tolerance against the compounds that are to be tested.…”

“…The community tolerance remains measurable as community characteristic and can be quantified using short-term toxicity tests in the laboratory. The metal content and soil properties are shown in Table 7 Land fatty acid analysis [19], acetate mineralization [20], ammonia oxidation [21], plate counts [11], and Biolog microtiter plates [21][22][23]. An increase in community tolerance (compared to the baseline tolerance from reference data), suggests that the community is affected adversely by a specific toxicant [13].…”

Copper-Induced Modifications of the Trophic Relations in Riverine Algal–bacterial Biofilms

“…An increase of the tolerance to toxicants in polluted environments has been observed in other aquatic and terrestrial systems, indicating the replacement of Cu-sensitive organisms by more tolerant ones [23,[34][35][36]. The treatment-related change of CLPPs and the increased bacterial tolerance to Cu showed that the heterotrophic community adapted to the experimentally applied conditions.…”