Evaluating chronic risk

Since the late 1960s, regulations on chemical substances have required manufacturers to identify the dangers inherent in the substances they produce. However, it was not until the early 1990s that it became mandatory to evaluate the dangers of substances before they come onto the market, in the aim of both protecting human health and conserving natural environments.

The evaluation of ecological and health risk on the scale of a geographic zone or territory (urban or rural area, municipality or group of municipalities, region, etc.) began with the decree of July 16, 1976, on facilities classified for environmental protection. This law mandates hazard studies, diagnoses of the direct and indirect effects of an industrial facility on the surrounding natural environment and on the health of local residents.

In France during the 1980s and 1990s, principles for evaluating risks to ecosystems were gradually imposed in highly varied contexts (industrial emissions, polluted soils, phytosanitary practices in agriculture, waste treatment, etc.). Methodological foundations for evaluating health risks due to the presence of chemical substances in the environment were established during these early decades, and by the turn of the 21st century had become standardised and widespread.

Since 2000, health and ecological approaches have been the subject of methodological reflection and political action, as evidenced by the first national health-environment plan in France in 2004.

Domains in which chronic risk evaluation is applied

The evaluation of risks to natural environments and human health can be divided into three major approaches depending on the objective.

• The “substance” approach covers effects of a substance considered in isolation on its surroundings; for example, a chemical product intended for sale. This approach is used in the context of chemical product safety (REACH regulations). It aims to determine, in advance, the probability of the substance having dangerous effects on natural surroundings or human health, throughout its lifecycle: from production, formulation and use to recycling and final elimination.
• The “matrix” approach (the environmental matrix, the medium in which a chemical substance is found) deals solely with the effects of contamination by chemical molecules in situ. The effects can be both to natural surroundings (flora and fauna) and the health of human populations.  This evaluation approach is used during the recycling and recovery of waste or polluted sediment. It also involves implementing information and labelling policies for consumer products that may have an impact on indoor air quality: decorative products, indoor air fresheners, household products, etc.
• The “spatial” or “territorial” approach deals with the effects of all substances present in a given space or in a given geographic area. For example, this approach is used in environmental monitoring and conservation policy (EU Water Framework Directive), in the management of polluted sites, to regulate at-risk industrial activities (health risk evaluation), and in conducting studies at the regional level to identify environmental inequalities across the country. The approach to evaluating risk must consider effects (or environmental stresses) at multiple organizational levels of a given area: individuals, groups and populations for health risks; and individuals, communities and ecosystems for ecological risks. The evaluation takes into consideration direct effects on the individual, major changes in the dynamics of a population or group, and disturbances in the interactions between species.

Stages in the chronic risk evaluation process

Nowadays, despite their objectives, objects of study, terminology, assessment criteria and practices, the approaches to ecological risks and health risks have four major steps in common. The first two involve identifying dangers, while the next two deal strictly with evaluating the risk.

• The first step is identifying the dangers of substances is determining the effect associated with potential exposure on each target. This entails identifying the effect a substance may have on living organisms (human organs, sensitive plant or animal species, etc.) due to its intrinsic properties: toxicity to humans and/or the environment, mode of action, types of effects (carcinogenic, reprotoxic, bioaccumulative, etc.). Research into the toxicity of a substance relies on a range of sources: [regulatory] safety data sheets (FDS), technical and scientific texts on substances, data obtained in emergency or accidental situations ...
• The second stage entails determining the qualitative and quantitative severity of these harmful effects. A relationship is established between the quantity (concentration) of a dangerous substance and the changes it induces on the target environment or organism. In health risk management, this relationship is known as the “dose-response relationship” and is expressed using toxicity reference values (TRVs). Each substance has multiple TRVs based on whether there is a threshold for the effect in question, the type of “critical effect” (first harmful effect to occur as dose is increased), exposure pathway and exposure duration. In environmental risk management, a Predictive No Effect Concentration (PNEC) is usually estimated based on the results of laboratory biotesting. These tests should be conducted on species representing at least three levels of an ecosystem’s food chain (the trophic chain). For example, algae, invertebrates and fish for aquatic environments. The main difficulty lies in extrapolating results that were obtained on a small scale and under controlled conditions to real-life situations. Studies may also use medium-scale experiments (mesocosms, for instance) or studies conducted in the field (in situ). Depending on data availability, these reference values also integrate safety factors.
• The third step is estimating exposure, which is the quantitative estimation of the potential concentrations of substance present in the environment of exposed organisms, identifying the pathways by which the organisms are exposed to the substance, studying how the substance is transferred into that environment from the emission source, and accounting for the daily use and cultural practices of humans exposed.
• For ecosystems, estimating exposure entails calculating the Predictive Environmental Concentration (PEC). In terms of human health, it is expressed in “average daily dose” (ADD) for ingestion, and “average inhaled concentration” (CI).
• This quantification can be done based on measured data (in the organism and/or environment) and based on forecasts (modelling) for calculating levels and concentrations of exposure.
• The final step is the risk characterization phase, which uses the estimates of effects of exposure to express the probability of an impact on health or ecosystems. It consists of calculating indicators which express the relationship between a substance’s effect and exposure. In health management, these indicators (“hazard quotients” for effects with thresholds and “high individual risk” for effects without thresholds) are calculated for each substance, exposure pathway and category of population exposed. A risk is deemed of concern when the indicator exceeds a predefined value (greater than 1 for hazard quotients and greater than 0.0001 for high individual risk). For ecosystems, the most commonly used method is the risk ratio or quotient, which is based on the relationship between concentration with a predicted effect and concentration without predictable effect. If the PEC/PNEC ratio is less than 1, the risk is deemed acceptable; if it is greater than 1, the risk is deemed unacceptable.