It can directly affect the value of an injury claim because it may show that a chemical actually entered a person's body, not just that the person was near a spill, workplace hazard, or contaminated water source. That evidence can strengthen causation, support damages, and help separate mere environmental presence from measurable human exposure. It can also limit a claim if the testing does not match the substance alleged, was taken too late, or shows levels consistent with background exposure rather than a harmful dose.

Biomonitoring is the measurement of chemicals, their metabolites, or related biological markers in human tissues or fluids such as blood, urine, hair, breast milk, or, less commonly, nails or breath. The goal is to quantify internal dose: what was absorbed into the body. Depending on the substance, results may be compared with reference ranges, occupational standards, or public-health action levels. Biomonitoring does not automatically prove illness, source, or legal fault; it is one part of an exposure assessment.

In Michigan toxic-exposure cases, biomonitoring may be relevant in claims involving lead, PFAS, solvents, or industrial metals. Michigan's Public Health Code, 1978 PA 368, and state and local health agencies may use blood testing and related surveillance for public-health response, but no single statewide biomonitoring result automatically establishes civil liability. In litigation, timing, chain of custody, laboratory method, and expert interpretation are often decisive.