A Protocol for Assessing Potential Adverse Effects of Substances in Soil on Designated Terrestrial Ecosystems
SR (99) 01 F
This report describes the output of a research project commissioned by SNIFFER to develop the first level of a technical methodology to derive site specific numeric targets for contaminants in soil, to assist in the protection of specific terrestrial ecosystems.
The results of this project are actually presented in two reports. This report, ‘A Protocol for assessing potential adverse effects of substances in soil on designated terrestrial ecosystems’ and ‘A Guidance Manual for assessing potential adverse effects of substances in soil on designated terrestrial ecosystems’.
The project was primarily aimed at meeting the needs of regulators concerned with the remediation of contaminated land under Part IIA of the Environmental Protection Act 1990. However, the output of this research project may also be of use to others concerned with the assessment and management of land which is contaminated and adversely impacting on ecosystems within a statutorily designated location. The method also has the potential to be applied to non-designated sites. The method was required to be transparent, robust, rapid to carry out, practical and scientifically defensible. The method has been developed on the basis that a preliminary risk assessment will have already been conducted and the substances deemed to present a risk of adverse effects on the ecosystem have been identified.
In the derivation of numeric targets for contaminated land to protect ecosystems, information is required on three key elements:
- the toxicity of contaminants present in soil to species representative of the indigenous populations and communities to assess the effects on ecosystem structure;
- the effects of contaminants present on fundamental microbial processes such as nutrient and energy cycling to assess effects on ecosystem function;
- the potential for secondary poisoning of organisms higher in the food web (for example birds and mammals) by ingestion of contaminants, which have bioaccumulated at lower levels of the food web.
In the first level of the proposed method the protection of ecosystem structure and function are considered to be equally important in the derivation of numeric targets and preliminary targets for both are derived. No preliminary numeric target for secondary poisoning is derived but rather it is identified as an issue for consideration at a higher level of the method.
The overall strategy comprises seven key steps:
- collection and assessment of data on the soil at the contaminated site (for example pH, % organic matter, % clay, cationic exchange capacity, background concentrations, essential concentrations);
- collation and assessment of environmental data (contaminant fate and behaviour, effects on individual species and microbial processes and the potential for bioaccumulation) and a consideration of the acceptability of the available data for deriving numeric targets;
- derivation of a preliminary numeric target for the protection of ecosystem structure (NTS). The derivation of a preliminary numeric targets is carried out using a ‘probabilistic’ approach if > 4 values for effects on four different taxa (including at least one plant or invertebrate species) are available. The probabilistic approach involves applying an uncertainty factor to the mean of the species sensitivity distribution using an established modelling approach. If values are only available for effects on 2-3 different taxa (including at least one plant or invertebrate species) then a "deterministic" approach is used in which an uncertainty factor is applied to the lowest of the values. No preliminary NT values are derived if data for effects on only one taxa are available.
- derivation of a preliminary numeric target for the protection of ecosystem function (NTF). The derivation of a preliminary numeric target is carried out using a ‘probabilistic’ approach if > 4 values for effects on four microbial processes (including nitrogen fixation or nitrification) are available. The probabilistic approach involves applying an uncertainty factor to the mean of the species sensitivity distribution using an established modelling approach. If values are only available for effects on 2-3 different microbial processes (including nitrogen fixation or nitrification) then a "deterministic" approach is used in which an uncertainty factor is applied to the lowest of the values. No preliminary NT values are derived if data for effects on only one microbial process is available. In certain instances where organic compounds act as a carbon source for microbes, NTF may not need to be derived.
- derivation of an overall site-specific numeric target as the lowest of the preliminary NT values;
- consideration of the need to incorporate the potential for secondary poisoning and comparison of the derived numeric target with;
- the site specific background concentration
- the limit of detection for the substance by the chosen analytical method
- the essentiality of the substance
7. consideration of any subsequent action based on the measured contaminant concentrations and the overall numeric target. The reviewer should use scientific judgement in assessing the appropriateness of the overall NT value for the site of concern.
Contaminated land, soil, terrestrial ecosystem, numeric target, plants, invertebrates, microbial processes, secondary poisoning
Copies of this report are available from the Foundation, price £15.00, less 20% to FWR Members.