Agricultural application of digestates derived from agricultural and municipal organic wastes: a health risk-assessment for heavy metals.

A Human-health Risk Assessment was performed for an agricultural site in North-East Italy undergone digestate application to (i) check the compliance of digestate land spreading with the Italian and European regulations on contaminated agricultural soils and (ii) evaluate how resulting risk estimations can be influenced by the applied modeling assumptions. The assessment estimated the risk related to adults and children intake of Heavy Metals (HM) contained in crops at concentrations estimated by a soil-plant transfer model based on the substance-specific soil-water partition coefficients. Eight different scenarios were investigated, according to different digestate type (from biowaste and agro-industrial byproducts), digestate application techniques and soil background concentrations. Non-risky situations resulted in all scenarios involving digestate application. The totality of calculated non-carcinogenic Hazard Indexes (HI) and carcinogenic total risk (RTOTC) resulted below 0.02 and 3E10-9, respectively. In contrast with the definition, non-carcinogenic risks were associated with the considered soil background concentrations, with HI s up to 1.7 for child receptors, while carcinogenic risk was calculated below the concern threshold (i.e., RTOTC < 10-5). Accordingly, this study highlighted (i) non-concerning situations related with lawful application of digestates and (ii) the need to improve the modeling of bioavailability to plant of HMs background content of soil.