Environmental Risk Assessment

Traditionally, risk assessment (RA) has been focused on threats to humans posed by industrial pollutants. In recent times there has been a shift to other types of hazards and affected objects. Environmental risk assessment (ERA) has already evolved into separate methodology under the general risk assessment framework.

When applied to a particular site and/or project, ERA procedures include several generic steps such as 'hazard identification', 'hazard assessment', 'risk estimation', and 'risk evaluation'. Despite rapid development of ERA guidance and wide support for the idea of tools integration, ERA is rather exclusion in environmental impact assessment (EIA) practice. In fact, the formal risk assessment follows the 'bottom-up' approach to assessing ecosystem-level effects. The assessor depends mainly on findings of laboratory toxicity testing that are extrapolated to higher levels of natural system hierarchy (from organisms to communities and even ecosystems) using various factors. Meanwhile, too many assumptions put a burden of high uncertainty on final quantitative risk estimates. Moreover, ecosystem risk assessments of this type are rather experiments than established practice. High costs and lack of required data are among key reasons for avoiding this approach by practitioners.

As a result, an EIA practitioner faces considerable difficulties while assessing impacts on ecosystems. On the one hand, there are legal requirements to assess fully ecological effects and best practice recommendations to undertake quantitative assessments where possible. On the other hand, many assessors lack tools and techniques to undertake estimations with a high degree of confidence and prove them to be scientifically defensive. Of importance, there are formal RA techniques for tackling the uncertainty (first, data uncertainty) in a clear and explicit manner and its quantification, to increase impact predictability (the two most widely known are sensitivity analysis and Monte Carlo error analysis).

As to assessment of ecosystem impacts, the proposed integration model implies using formal ERA methodology. The general ERA framework suggested by the US Environmental Protection Agency is depicted in Figure 1. It is similar to schemes followed by other counties.

Ecological risk assessment in EIA is to evaluate the probability that adverse ecological effects will occur as a result of exposure to stressors (stressor is a chemical, physical, or biological agent that can cause adverse effects in nonhuman ecological components ranging from organisms, populations, and communities, to ecosystems) related to a proposed development and the magnitude of these adverse effects. A lion's share of site-specific

Figure 1 The framework for ecological risk assessment.

ERAs was concerned with chemical stressors - industrial chemicals and pesticides.

In formal ERA framework, three phases of risk analysis are identified: problem formulation, analysis, and risk characterization followed by 'risk management'. The analysis phase includes an 'exposure assessment' and an 'ecological effects assessment' (see Figure 1).

Biogeochemical Approaches to Environmental Risk Assessment

It is well known that biogeochemical cycling is a universal feature of the biosphere, which provides its sustainability against anthropogenic loads, such as acid forming compounds of S and N species, heavy metals and persistent organic pollutants (POPs). Using biogeochemical principles, the concept of 'critical loads' (CLs) has been firstly developed in order to calculate the deposition levels at which effects of acidifying air pollutants start to occur. A UN/ECE (United Nations/Economic Committee of Europe) working group on sulfur and nitrogen oxides under long range transboundary air pollution (LRTAP) convention has defined the critical load on an ecosystem as: ''A quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge.'' These critical load values may be also characterized as ''the maximum input of pollutants (sulfur, nitrogen, heavy metals, POPs, etc.), which will not introduce harmful alterations in biogeochemical structure and function of ecosystems in the long-term, i.e. 50-100 years.''

The term 'critical load' refers only to the deposition of pollutants. Threshold gaseous concentration exposures are termed 'critical levels' and are defined as ''concentrations in the atmosphere above which direct adverse effects on receptors such as plants, ecosystems or materials, may occur according to present knowledge.''

Correspondingly, transboundary, regional, or local assessments of critical loads are of concern for optimizing

Load

Target load with Target load accepting safery factor some effect

Present load

Figure 2 Illustration of critical load and target load concepts.

Load

Target load with Target load accepting safery factor some effect

Present load

Figure 2 Illustration of critical load and target load concepts.

abatement strategy for emission of polutants and their transport (Figure 2).

The critical load concept is intended to achieve the maximum economic benefit from the reduction of pollutant emissions since it takes into account the estimates of differing sensitivity of various ecosystems to acid deposition. Thus, this concept is considered to be an alternative to the more expensive best available technologies (BAT) concept. Critical load calculations and mapping allow the creation of ecological-economic optimization models with a corresponding assessment of minimum financial investments for achieving maximum environmental protection.

In accordance with the above-mentioned definition, a critical load is an indicator for sustainability of an ecosystem, in that it provides a value for the maximum permissible load of a pollutant at which risk of damage to the biogeochemical cycling and structure of ecosystem is reduced. By measuring or estimating certain links of bio-geochemical cycles of sulfur, nitrogen, base cations, heavy metals, various organic species and some other relevant elements, sensitivity of both biogeochemical cycling and ecosystem structure as a whole to pollutant inputs can be calculated, and a 'critical load of pollutant', or the level of input, which affects the sustainability of biogeochemical cycling in the ecosystem, can be identified.

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