67 For human health risk assessment, effects are distinguished as non-carcinogenic and carcinogenic. For non-carcinogenic effects, the existence of threshold levels is assumed, and toxicity is expressed through reference doses or reference concentrations derived from experimental or epidemiological studies, incorporating uncertainty factors to account for interspecies differences and human variability. For carcinogenic substances, a no-threshold assumption is applied, and dose–response relationships are described using slope factors to estimate incremental lifetime cancer risk as a function of exposure. Toxicological reference values are obtained from official and up-to-date sources (MINAM, 2015). Exposure assessment quantifies how much contaminant reaches the receptor and through which pathways. Closure-related HHRAs apply a source–pathway–receptor framework, considering lifetime exposure horizons (≥70 years), multiple exposure routes (ingestion, dermal contact, inhalation, and consumption of locally produced food), and probabilistic modeling where temporal uncertainty is significant. The objective is not to achieve zero risk, but to demonstrate that risks are acceptable and compatible with the intended future land use and regulatory thresholds. For ecological risk assessment, toxicological analysis is based on concentration– response relationships, observed and no-observed effect levels, and causal evidence. In the absence of site-specific data, bioassays, biomarkers, and internationally recognized reference values are used. Ecological exposure is defined as the spatial and temporal co-occurrence of contaminants and receptors, integrating habitat characteristics, exposure pathways, and representative scenarios. Contemporary ERAs apply multiple lines of evidence —including monitoring data, bioassays, ecological benchmarks, and transport modeling— to assess the physical, chemical, and biological stability of mining components over timescales ranging from decades to centuries. 2.4 Risk characterization Risk characterization represents the final phase of the assessment, integrating toxicity and exposure results to estimate the likelihood of adverse effects on human and ecological receptors. For human health, non-carcinogenic risk is expressed using hazard quotients and hazard indices, defined as the ratio between estimated exposure doses and reference doses. Exceedance of reference values indicates potential concern, and exceedances greater than one order of magnitude are typically interpreted as unacceptable risk (MINAM, 2015). Carcinogenic risk is quantified as incremental lifetime cancer risk, calculated by multiplying estimated exposure doses by slope factors; risks exceeding 1 × 10⁻⁴ are generally considered unacceptable and warrant specific management actions.
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