Authored by: Rimkus Forensics Marketing Team
An environmental exposure event, whether a release, a contamination discovery, or a claim alleging harm, puts insurance professionals and attorneys on the clock to establish what happened before evidence, records, or exposure pathways degrade. Environmental exposure investigations evaluate which contaminants are present, how they migrated, potential sources of release, and whether the available evidence is scientifically consistent with the alleged harm.
The strength of those findings depends on how the investigation is built from the outset: documented sampling protocols, defensible source identification, and dose-response analysis that can withstand opposing expert scrutiny. Liability under CERCLA may attach to the full scope of contamination-related harm when that harm is legally indivisible, though it may be apportioned when a party can establish a reasonable basis for divisibility, making the quality of the underlying technical record a direct factor in claims and litigation outcomes.
This article covers what an environmental exposure investigation establishes, how sampling, source identification, and dose-response analysis are conducted, and where regulatory standards and case law set the limits of what investigation findings can prove.
Key takeaways: Evaluating contamination and exposure
Environmental exposure investigations provide technical information that may help stakeholders evaluate contaminant sources, migration pathways, potential exposures, and claimed health effects.
What the investigation must establish
- Causation in toxic tort cases splits into general causation (the substance can cause this harm) and specific causation both often require dose-response analysis
- Regulatory thresholds such as National Ambient Air Quality Standards (NAAQS) and drinking-water Maximum Contaminant Levels (MCLs) are regulatory benchmarks, not proof that an individual experienced a harmful dose or a particular health effect
- PFAS require specialized evaluation: the 2024 designation of PFOA and PFOS as CERCLA hazardous substances made CERCLA response and cost-recovery authorities applicable to releases of those substances, subject to statutory defenses, divisibility principles, enforcement discretion, and other case-specific considerations
How investigations typically proceed
- Sampling plans generally include documented collection, handling, preservation, quality-control, and chain-of-custody procedures appropriate to the investigation
- Fate and transport modeling may help trace contaminant migration from source to receptor
- Chemical fingerprinting can help distinguish potential contaminant sources and evaluate their possible contributions to a mixed release
- Dose-response analysis and biomonitoring, such as blood level testing, may help evaluate whether documented exposure levels are consistent with reported health outcomes
Rimkus offers multidisciplinary expertise in environmental health sciences for air, water, and soil contamination matters. Contact us to discuss a specific matter.
What is an environmental exposure investigation?
The Agency for Toxic Substances and Disease Registry (ATSDR) defines an exposure investigation as a biological or environmental sampling effort designed to fill a data gap needed to make public health decisions. Similar analytical frameworks apply when exposure questions are evaluated for litigation or insurance purposes.
The five-element exposure pathway examines a contaminant source, environmental fate and transport, an exposure point, an exposure route such as ingestion, inhalation, or dermal contact, and a potentially exposed population. ATSDR classifies pathways as completed, potential, or eliminated depending on whether all five elements are present. A completed pathway means exposure may have occurred or may be occurring; that classification alone does not establish that health effects resulted.
Forensic investigators build a conceptual site model that maps contaminant sources, transport pathways, exposure points, exposure routes, and potentially exposed populations and informs sampling design and subsequent analysis.
Why do environmental exposure claims carry significant stakes?
CERCLA liability is generally described as strict and retroactive and may be joint and several when the harm is indivisible. Under the EPA’s enforcement framework, four classes of potentially responsible parties may face cleanup obligations: current owners and operators, past owners and operators at the time of disposal, generators who arranged for disposal or transport, and transporters who selected the disposal site. A party that does not comply with an EPA cleanup order may face civil penalties and, in certain circumstances, liability for additional response costs or punitive damages under CERCLA.
In fiscal year 2025, EPA concluded 2,127 civil enforcement cases, assessed over $1.2 billion in civil penalties and criminal fines, and charged 156 defendants in criminal cases. The PFOA and PFOS CERCLA designation, discussed in more detail below, has further expanded the pool of potentially responsible parties and added a new category of technically demanding investigation to an already complex enforcement environment.
What types of environmental exposure are investigated?
Environmental contamination reaches human receptors through three primary media: air, water, and soil. Each presents distinct sampling challenges, exposure routes, and forensic considerations. PFAS require separate treatment given their cross-media mobility and the regulatory developments discussed below.
Air
Air exposure cases commonly involve volatile organic compounds (VOCs) such as trichloroethylene (TCE) and benzene, hydrogen sulfide, and particulate matter. Vapor intrusion, where subsurface VOCs migrate into indoor air, is a recognized exposure mechanism that may elevate indoor concentrations well above what ambient outdoor measurements would suggest.
Water
Groundwater plume investigations often target chlorinated solvents, PFAS compounds, and fuel-related contaminants. Surface water exposure may involve industrial discharges regulated under the Clean Water Act’s National Pollutant Discharge Elimination System (NPDES).
Soil
Metals from industrial deposition (i.e. lead paint), hydrocarbons, and pesticides are common soil contaminants in forensic investigations. Exposure routes include ingestion, dermal contact, and inhalation of fugitive dust. Investigators typically model all three routes to characterize cumulative exposure.
PFAS
Per- and polyfluoroalkyl substances (PFAS) present a distinct category in environmental exposure investigations because they migrate across all three media simultaneously. PFAS are highly mobile in groundwater, resistant to conventional remediation methods, and capable of forming extensive plumes that travel far from their release point. That combination makes source identification and fate-and-transport modeling particularly important when evaluating contaminant origins and relative source contributions.
The forensic significance of PFAS increased substantially after the 2024 CERCLA designation of PFOA and PFOS, including their salts and structural isomers, as hazardous substances, effective July 8, 2024. The designation made CERCLA reporting, response, enforcement, and cost-recovery provisions applicable to qualifying releases of those substance.
EPA stated in September 2025 that it was retaining the designation. Although CERCLA claims may raise concerns for entities that receive or manage PFAS-containing materials, EPA has stated that it intends to consider equitable factors and exercise enforcement discretion for certain passive receivers, including municipal water utilities, publicly owned treatment works, municipal landfills, municipal airports, local fire departments, and farms. Potential liability depends on the facts, the party’s statutory status, applicable defenses, divisibility, and the type of claim asserted.
Investigations of PFAS releases may require targeted analytical methods using isotope-dilution mass spectrometry, supplemented where appropriate by techniques such as the total oxidizable precursor (TOP) assay to evaluate the possible presence of oxidizable precursor compounds not captured by the targeted analysis. Source attribution in mixed-plume settings is technically demanding, and the data collected during early investigation phases may significantly affect the ability to distinguish sources and evaluate their relative contributions.
How is an environmental exposure investigation conducted?
Each phase of a forensic environmental investigation, from sampling design through data interpretation and reporting, shapes the conclusions the resulting record can support.
Sampling, testing, and chain of custody
Samples collected during a forensic environmental investigation should be documented from collection through analysis and storage using chain-of-custody procedures appropriate to the project. Gaps in documentation may raise questions regarding sample identity, handling, integrity, or interpretation.
Quality assurance and quality control (QA/QC) planning commonly includes establishing Data Quality Objectives (DQOs) before sampling begins. Inadequate documentation of the investigation’s objectives, detection limits, sampling design, and decision criteria may limit how confidently the resulting data can be interpreted. Sampling decisions made before collection often determine what questions the data can reasonably answer.
Biomonitoring, the measurement of chemicals or their metabolites in blood, urine, or other human specimens, may supplement environmental sampling. As EPA notes, biomarkers of exposure do not by themselves establish causation of disease. Bridging from biomarker levels to alleged injury requires dose-response data, epidemiological evidence, and individual susceptibility analysis.
Source identification and fate and transport
Source identification may help connect contamination detected at a site or receptor to one or more potential sources. Chemical fingerprinting uses techniques such as gas chromatography-mass spectrometry (GC-MS), compound-specific stable isotope analysis (CSIA), and isotope ratio mass spectrometry to characterize contaminant composition and compare samples to potential sources. Chemical fingerprinting may help evaluate mixtures of source signatures and estimate the relative contribution of potential sources when the analytical, temporal, and hydrogeologic evidence is sufficient.
No single fingerprinting result closes the question. The analysis generally gains weight when chromatographic, isotopic, and hydrogeologic lines converge. Investigations typically develop multiple independent lines of evidence. Fate and transport modeling then traces contaminant migration through groundwater flow models, soil-to-groundwater transport tools, and air dispersion models to connect source to receptor.
What standards and regulations apply to environmental exposure?
Regulatory thresholds function as analytical reference points in forensic investigations, not as proof of harm. NAAQS primary standards are set with a margin of safety covering the most vulnerable populations; an exceedance triggers a regulatory response but does not establish that an individual plaintiff suffered injury. ATSDR comparison values used in screening similarly do not indicate that health effects are likely.
Key federal statutory frameworks that may apply to environmental contamination include CERCLA, the Resource Conservation and Recovery Act (RCRA), the Clean Air Act, the Clean Water Act, and the Safe Drinking Water Act (SDWA), along with other federal, state, and local requirements depending on the contaminants and activities involved. CERCLA’s hazardous substance definition incorporates substances designated under several of those statutes, creating overlapping liability frameworks that can complicate allocation analysis.
Enforceable standards versus health-based goals
The distinction between enforceable Maximum Contaminant Levels (MCLs) and non-enforceable Maximum Contaminant Level Goals (MCLGs) under the SDWA is important in environmental exposure assessment. MCLGs are health-based goals set at levels below which no known or expected health risk is identified, with a margin of safety. MCLs are enforceable standards set as close to the corresponding MCLG as feasible after considering treatment technology and cost. Neither value, by itself, establishes an individual’s exposure dose or proves that a particular health effect occurred.
How do investigation findings support exposure and claims evaluations?
Technical findings from environmental exposure investigations may inform source attribution, exposure assessment, causation analysis, claims evaluation, and regulatory review. The strength of those findings depends on whether the underlying data were collected and analyzed using appropriate, documented, and scientifically supportable methods.
Establishing general and specific causation
Toxic tort litigation typically involves two distinct causation showings. General causation asks whether the substance can cause the type of harm alleged. Specific causation asks whether this plaintiff’s exposure caused this plaintiff’s injury.
The New York Court of Appeals in Parker v. Mobil Oil Corp. required plaintiffs to provide reliable expert evidence of exposure and a scientific basis connecting the substance to the alleged illness at the levels experienced, without requiring a precise numerical dose in every case. Federal courts have similarly required that experts provide evidence of exposure dose, amount, duration, intensity, or other reliable proof of substantial exposure rather than relying on the mere presence of a contaminant. Scientific knowledge of a harmful exposure level, combined with evidence that the plaintiff experienced such exposure, usually represents the minimum showing federal courts have required.
The role of forensic environmental experts
When environmental opinions are used in legal proceedings, they are generally expected to be based on sufficient facts or data, reliable scientific methods, and reliable application of those methods to the facts being evaluated. Investigators should clearly document sampling design, quality controls, assumptions, limitations, exposure estimates, and the scientific basis for their conclusions.
Regulatory exceedances and temporal associations should not be treated as substitutes for exposure assessment, dose-response analysis, or evaluation of plausible alternative causes. The strength of an environmental causation opinion depends on the quality of the exposure evidence and the scientific basis connecting the estimated exposure to the alleged outcome.
When forensic expertise clarifies the technical record
Complex environmental exposure matters often involve competing source and causation hypotheses, incomplete historical information, and significant time pressure to preserve representative evidence. Forensic investigation can help develop the technical record needed to evaluate those issues, from initial sampling design through analysis and reporting.
With 40+ years of experience, 100+ offices worldwide, and 900+ experts on staff, Rimkus provides multidisciplinary expertise for air, water, and soil contamination matters through environmental health sciences and forensic investigation. Contact our team to discuss a specific environmental exposure matter.
Frequently asked questions about environmental exposure investigations
How do uncertainty factors differ between occupational and environmental exposure assessments?
Uncertainty factors in environmental non-cancer assessments often use composite values in the range of 100 to 1,000 to protect the general population over long-term, continuous exposure durations, whereas occupational assessments may use smaller, case-specific factors reflecting working-age populations and workday-based exposure scenarios. Acceptable risk thresholds also differ: occupational frameworks often permit cancer risk levels between 10⁻³ and 10⁻⁴, compared to environmental standards that typically target 10⁻⁵ or 10⁻⁶.
How do agencies handle situations where a responsible party is unwilling or unable to act promptly?
When agencies determine that a responsible party will not or cannot act quickly enough, they typically escalate from cooperative compliance to coercive measures, issuing unilateral administrative orders, imposing accelerating civil penalties, or suspending operating permits. If those measures fail or delay threatens imminent harm, statutes may authorize agencies to perform remediation directly and recover costs through liens, cost recovery litigation, or treble damage provisions under the applicable liability framework.
What factors influence the bioavailability of contaminants in soil?
Bioavailability describes the fraction of a soil contaminant that organisms can absorb or that remains mobile in the environment, and soil properties, contaminant chemistry, and environmental conditions together govern whether contaminants bind to soil particles or remain dissolved in pore water. Key factors include organic carbon content, clay and silt content, cation exchange capacity, pH, moisture, redox conditions, aging time, and contaminant-specific properties such as molecular size, charge, polarity, and chain length.
This article is intended to provide general information and insights into prevailing industry practices. It is not intended to constitute, and should not be relied upon as, legal, technical, or professional advice. The content does not replace consultation with a qualified expert or professional regarding the specific facts and circumstances of any particular matter.