Formulating a Soil Pollution Risk Assessment and Characterization

Soil, the uppermost portion of the Earth’s crust, is a product of weathering and physical, chemical, and biological processes. The soil is made up of mineral particles, organic matter, water, air, living organisms. [1] It plays a significant role as it offers shelter and habitat for countless and various organisms, serves as incubation and living medium for plants. It plays a vital role in the universal cycle of material flow between the atmosphere, lithosphere, hydrosphere, and biosphere. [2] Because of this, the soil also bears the most considerable onus of environmental pollution. There are a number of ways and methods to pollute it. Hence, there is an urgency to provide a solution for controlling soil pollution to preserve its fertility and increase its productivity. [3]

Pollution is defined as an adverse, undesirable change in the physical, chemical, and biological characteristics of soil, air, and water, which affects human life, plants and animals, industrial development and living conditions, and cultural assets. A pollutant is something detrimental to the health, comfort, property, and environment of people. This can be introduced by sewage, waste, accidental discharge, or byproducts of manufacturing processes. [3]

Environmental Risk Assessment

A risk assessment is a useful tool to characterize the risks of soil pollution, which is also helpful in remediation efforts. The Environmental Protection Agency (EPA) uses this method to describe the nature and extent of health risks to humans and an ecological life from chemical contaminants, irritants, and hazards that may be present in the environment.

Risk is considered to be the change of bringing about harmful effects to the health of humans or ecological systems due to exposure to environmental stressors. A stressor is defined as any physical, chemical, or biological agent that can provide an adverse effect. Natural resources or entire ecosystems, including plants and animals, and the environment where they interact can also be affected by stressors. [4]

Ecological Risk Assessment

Risk is considered to be the change of bringing about harmful effects to the health of humans or ecological systems due to exposure to environmental stressors. A stressor is defined as any physical, chemical, or biological agent that can provide an adverse effect. Natural resources or entire ecosystems, including plants and animals, and the environment where they interact can also be affected by stressors. [4]

ERA has two major types, predictive and descriptive. Predictive risk assessment covers how hazardous substances are handled, such as pesticides and chemicals. The descriptive method evaluates changes in population ecosystems in polluted areas. The first type is based on laboratory or controlled and semi-manipulated field studies as it relates to real-world situations while the other is more specific as it monitors ecosystem changes in contaminated soils.

Components of an ecological risk assessment and risk characterization

Problem Formulation

The first step of risk assessment is problem formulation. In this step, the goal, scope, and focus of the assessment are identified. Systematic planning is critical in this step to identify the significant factors to be evaluated which is linked to the regulatory and policy context of the organization. An activity with an observed ecological effect or identification of a stressor can start the risk assessment. The problem formulation process consists of:

• Initial characterization of exposure and ecological effects
• Evaluating stressor characteristics
• Identifying the ecosystem at risk and ecological effects observed

These shall be followed by the identification of assessment and measurement endpoints. A conceptual model shall be developed to describe how a given stressor might affect the ecological components of the environment. It elaborates on the relationships among the measurement endpoints and the assessment, the data measured, and the strategies that will be used to analyze the data and serves as input to the analysis phase of the assessment. [5]

Exposure Assessment

The exposure assessment identifies the path by which soil contaminants may be congested by the receptor. This information is combined with receptor characteristics in order to estimate the contaminant uptake. The characterization of exposure evaluates the interaction of the stressor with the ecological component. This analysis involves the measurement of concentrations or amounts of a stressor and combines them with assumptions about co-occurrence, contact, or uptake.

Statistical methods are used in the characterization of exposure and ecological effects. Assumptions and data set characteristics are often employed. However, professional judgment is regularly required to evaluate the results with biological significance or impact.  [5]

Toxicity Assessment

Evaluation of exposure is then combined with information on the inherent toxicity of the chemical to predict the probability, nature, and magnitude of the adverse health effects that may occur. [6] Hence, this step evaluates the relevant effects data, analyzes the ecological response in terms of stressor –response determinations or extrapolations and causal evidence evaluation, and develop a stressor-response profile. [9]

Toxicity testing is a science of comparing the hazards of chemicals with one another and for determining its effects on test organisms. Toxicity assessment identifies the effects of various contaminants in soil and the organisms present in it to reveal the chemical properties of the contaminants and their interaction with unique soil components. The bioavailability and toxicity of contaminants depend on the ability of the soil for adsorption, transformation, metabolism, storage, sequestration, and accumulation of the contaminant. A meaningful hazard assessment needs a standardized testing method. [9]

Risk Characterization

Risk characterization is the final step in the process. The exposure and toxicity assessment are compared with the uptake rate to determine whether or not an adverse effect is likely to occur. The objective of having risk characterization is to communicate the key findings of the exposure and toxicity assessment and use it in combination with other information in evaluating options for rules, regulations, and negotiated agreements in terms of economics, public perception, social values, and policies. [3] [8]

The risk may be determined qualitatively or quantitatively or both based on the data obtained from the integrated results of exposure and toxicity assessments and should be connected to the assessment endpoint identified in the problem formulation phase. This includes the following:

• A summary of the assumptions made during the assessment
• The strengths and weaknesses of the evaluation
• The ecological significance of the considered risks in terms of type, magnitude, spatial and temporal patterns, causes and effect relationships, and the likelihood of recovery.

In the remediation of polluted soil, ensuring that contaminants are contained, and exposure to receptors should be prevented is vital. This happens when remediation options are subpar with industrial land-use objectives. From the assessment of risks, a containment system can be provided to address soil pollution. This mechanism should be periodically inspected and monitored. [3]

Soil pollution is indeed an issue that deserves serious attention. A risk assessment is an excellent tool to characterize the risks involved in soil pollution and can be an excellent guide in remediation efforts and ultimately generating science-based risk management decisions.