Deriving chronic species sensitivity distributions for PAHs in soil: a sublethal endpoint-based approach for...

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants ubiquitous in anthropogenically impacted soils, where they represent a chronic source of ecological risk for soil-dwelling organisms. Although total soil PAH concentrations constitute the primary diagnostic tool in contaminated site management, the derivation of ecologically meaningful alert values has been hampered by the predominance of acute and median-effect endpoints in available ecotoxicological datasets. The present study addresses this gap by developing chronic Species Sensitivity Distributions (SSDs) for five priority PAHs, Benzo[a]pyrene, Fluoranthene, Fluorene, Phenanthrene, and Pyrene, in terrestrial soil, based exclusively on sublethal endpoints (EC10, EC20, LOEC, NOEC) compiled from a systematic literature search across major ecotoxicological databases and peer-reviewed journals. A total of 43 chronic toxicity values were retained after applying a strict hierarchical selection protocol prioritising the most ecologically relevant endpoints, the longest exposure durations, and the most sensitive responses across plants, soil invertebrates, and micro-organisms. Five candidate statistical distributions were fitted by maximum likelihood for each PAH and final hazardous concentration estimates were derived using a model-averaging approach weighted by AIC, providing more robust uncertainty characterisation than single-model selection. HC5 values ranged from 0.57 mg kg^-1 (Pyrene) to 7.12 mg kg^-1 (Fluoranthene), while HC50 values spanned from 13.71 to 64.00 mg kg^-1, reflecting substantial interspecific variability in PAH sensitivity across the soil community. The wide confidence intervals observed for several PAHs highlight the critical need for additional chronic terrestrial ecotoxicological data. The derived thresholds are proposed as first-tier screening values within a tiered ecological risk assessment framework, intended to guide targeted ecotoxicological testing, prioritise site diagnosis, and support remediation decision-making for PAH-contaminated soils, complementing rather than replacing bioavailability-based assessment approaches.