Pollutant linkage

Standards can be expressed in various units, such as a load (mass/unit area), a dose (mass/body mass), or a concentration (mass/volume mass contaminant/mass soil). The use of a unit depends on the environmental compartment under consideration. We might consider the amount of pollution in water (a concentration), the consequences of equilibrium uptake by (or exposure to) a human (a dose), or the acceptable uptake by an ecosystem under steady conditions (the loading). The choice of unit depends on the point in a cycle or pollutant linkage at which we set the standard, as illustrated in Figure 3.1. 

The Pollutant Linkage Concept. A further concept within the definition—the contaminant-pathway-receptor approach—is elaborated in the statutory guidance. This concept has, in recent years, come to represent the predominant intellectual framework for risk assessment in general20 21 and has underpinned the development of contaminated land technical thinking. Unless a particular receptor could be harmed, through a defined pathway, by an identified contaminant, then land cannot be considered to meet the definition of contaminated land. 

The standard of remediation that needs to be achieved on a particular site is therefore whatever degree of risk management would be achieved by the use of the best practicable techniques for remediating each of the significant pollutant linkages on the site. 

This standard can then be used to evaluate any alternative approaches to remediation. These might, for example, be remediation approaches that sought to manage the risks for more than one identified significant pollutant linkage simultaneously. 

Monitoring. As suggested above, the Part IIA enforcement process can require action to be taken to monitor sites after remedial treatment action has been carried out. This obligation covers significant pollutant linkages that have already been identified, and is intended to pick up any changes that may occur in the condition of their component pollutants, pathways or receptors. 

Tests 4, 5 and 6— changes to substances , escaped substances and introduction of pathways or receptors —deal with different types of circumstances where one appropriate person has, in effect, left the site in a safe condition (notwithstanding the fact that he has caused or knowingly permitted a contaminant to be present) only for another person subsequently to change the condition of the land such that there is now a significant pollutant linkage. The tests were included in effect to transfer liability to the person who made the difference. 

In these circumstances, liability under Part IIA passes to the owner or occupier for the time being of the contaminated land in question 33—the current owner or occupier. However, this passage of liability does not take place where the significant pollutant linkage involved has controlled waters as its receptor in a case of that kind, the liability becomes orphan and responsibility for funding remediation passes to the taxpayer. 

The objective of this phase is to test the conceptual model developed in the Phase la assessment, to quantify the extent of sources and the possible transport of contaminants to receptors, and to classify confirmed pollutant linkages in terms of the risk presented to receptors. 

New information gathered from additional desk studies and any site investigation is then collated and used to provide more complete descriptions of the candidate source-pathway-receptor pollutant linkages identified in the Phase la report. Each linkage is considered separately and estimates are made of the extent and strength of the contaminant source, its connectivity to the receptor and the level of hazard that is presented to the receptor. Finally, a preliminary assessment is made of the potential harm that hazards may pose to the receptors. From this analysis it is likely that one or more pollutant linkages will be recognised as the... 

Successful conclusion of a Phase lb assessment depends on careful analysis of data to validate the conceptual model and identify those candidate pollutant linkages within each site zone that need to go forward for Phase 2 risk assessment. 

For the majority of sites, and certainly for the larger and more complex ones, zones within the site will have been identified that contain different types of source and that have distinct pollutant linkages associated with them. Each of these zones should have an associated conceptual model and be subject to risk assessment. 

The overall risk estimation should cover all the pollutant linkages identified, broken into site zones as appropriate. Details should be provided of source concentrations, with estimated confidence limits, the receptor characteristics and confirmation of the viability of the pollutant pathway. If generic guideline values are used, then their applicability should be supported. Clearly, full details need to be recorded of any models and data used to generate site-specific values for unacceptable risk, together with a commentary on assumptions that have been made in their application. 

All facts and conclusions relevant to the site need to be considered in the risk evaluation. Information from previous stages in the site assessment is collated and additional facts, particularly future site management details, may assist objective setting and the subsequent evaluation. All of the information available should be collated and ordered around its relevance to the evaluation objectives. For example, if an objective is to evaluate the risk to a groundwater abstraction well, then information that relates to the pollutant linkages to this receptor is collated and ordered. 

The general scheme for the technical evaluation is to take each receptor and to describe the level of risk that is presented to it by sources within the site. This leads to a set of key pollutant linkages that drive the overall risk from the site. By reviewing the criteria for identification of unacceptable risk for these key linkages—in terms of the certainty of threshold values, the impact of wrong risk assessment decisions on costs and the quality of site-specific information—a robust risk evaluation framework can be set for identifying unacceptable risk. 

Following risk evaluation, a consolidated risk assessment report is prepared, covering the description of the site and the pollutant linkages identified and the overall risk assessment, supported by validated data sets. This sets out unambiguously the main risks posed by the site and whether these are acceptable or not, and may identify preliminary options for dealing with unacceptable risks. 

Risks from contaminated land arise from pollutant linkages that present unacceptable risk to receptors. The purpose of risk management it to make changes that remove these unacceptable risks. This can be done in different ways the source of contamination may be removed or reduced the pathway by which contaminants reach the receptor may be broken or attenuated or the receptor can be removed or modified. 

Such uncertainties relating to exposure have been acknowledged in the recently introduced contaminated land legislation (see chapter by Lowe and Lowe) which describes the need for a pollutant linkage to be identified before land can be considered contaminated. In any investigation of the potential health effects of contaminated land, it is important that viable pollutant linkages are, at least, identified and, if possible, quantified to some extent. Even where an excess of disease may exist, if a specific hazardous exposure cannot be identified then no link can be made. 

The UK follows the widely recognised contaminant-pathway-receptor concept for assessing risks from contaminated land.4-8 This contaminant-pathway-receptor relationship is called a pollutant linkage.7 Receptors may, for example, be humans, surface water, groundwater, buildings, protected ecosystems or property, including livestock and crops. 

B.46 In following any such guidance on risk assessment, the local authority should be satisfied that it is relevant to the circumstances of the pollutant linkage and land in question, and that any appropriate allowances have been made for particular circumstances. 

B.47 To simplify such an assessment of risks, the local authority may use authoritative and scientifically based guideline values for concentrations of the potential pollutants in, on or under the land in pollutant linkages of the type concerned. If it does so, the local authority should be satisfied that ... 

Connected with the adoption of a risk-based methodology is the source-pathway-target or contaminant-pathway-receptor philosophy. This philosophy states that, in order for harm to have occurred, or for there to be a risk of harm occurring, contaminants must have been able to reach relevant receptors via specific environmental migration pathways. Where such a relationship exists between a contaminant, a pathway and a receptor at a site, a pollutant linkage is said to exist. 

In the initial stages of assessing a site, the contaminant-pathway-receptor philosophy can be used to exclude the site from further consideration on qualitative grounds when one or more of the three components is missing. For example, if the contamination is encapsulated in a sealed on-site cell which prevents the ingress or egress of precipitation, vapours and leachate, and animal or plant contact cannot occur, then no pathways exist and hence no pollutant linkages exist. The land cannot, therefore, be classified as contaminated land. 

In terms of assessing the existence or likelihood of ecological harm from pollutant linkages, the statutory guidance states that ... 

Any assessement made for these purposes should take into account relevant information for that type of pollutant linkage, particularly in relation to the ecotoxicological effects of the pollutant. ... 

There is also an option to perform biomonitoring, in the form of testing tissue samples for contaminants. As described previously, this can be used to confirm the existence of suspected pollutant linkages. 

---