Abstract
Metallic elements present in livestock manure as co-contaminants have the potential to cause terrestrial ecotoxic impacts when the manure is used as fertilizer on agricultural soils. The magnitude of this impact at country scale in Europe has, to date, not been quantified. Here, we address this knowledge gap by combining recently developed national emission inventories of Cd, Cu, Ni, Pb and Zn releases from manure with metal- and soil-specific comparative toxicity potentials (CTP) calculated for cropland grid cells at 1 × 1 km resolution for 33 European countries. The CTPs account for speciation in environmental fate, exposure and effects, including reduction in the solid-phase reactivity of a metal when it is associated with organic carbon present in the manure. Given the scarcity of inventory data at sub-national level, it was assumed that each unit area of cropland within a given country has the same probability to receive manure. The resulting CTPs span a range of several orders of magnitude reflecting the influence of soil type and properties on the speciation patterns and resulting CTP values. However, when combined with the use of manure in each European country, the resulting national impact scores were mainly explained by the total mass input of metal released to soil rather than by geographic variability in the CTP values. Simple linear regression is then sufficient to predict terrestrial ecotoxic impacts from input mass. Although some changes in ranking of metals and countries were observed, both mass- and impact-based comparisons between metals agreed that Zn and Cu are dominant contributors to total impacts, and that top contributing countries were those emitting the largest amounts of metals. Our findings show that spatially differentiated impact assessment is important for ranking of countries when differences in national emission inventories between countries are smaller than a factor of two (Ni), a factor of three (Cd, Cu, Zn) or a factor of four (Pb). In other cases, ranking of countries can be based on national emission inventories.
Highlights
Livestock manure is widely used by farmers to contribute to agricultural soil fertilization
The comparative toxicity potentials (CTP) account for speciation in environmental fate, exposure and effects, including reduction in the solid-phase reactivity of a metal when it is associated with organic carbon present in the manure
The median CTPs for terrestrial ecotoxicity calculated earlier by Owsianiak et al [11] for Cu and Ni emitted to air were equal to 1.4 × 103 and 2.4 × 103 m3pore water·day/kgtotal emitted to air, respectively, and ranged 3.5 and 3 orders of magnitude (95% variability intervals)
Summary
Livestock manure is widely used by farmers to contribute to agricultural soil fertilization. CTPs considering speciation were calculated for common cationic metals (with focus on Cu, Ni, and Zn) [11,15,16,17], but no country-scale assessment of the impacts resulting from metal emissions associated with the application of manure to agricultural soils considering these factors has, to date, been reported in the literature. We address the two aforementioned challenges with the overarching objective of assessing and comparing country-scale potential ecotoxic impacts resulting from the application of manure to European agricultural soils. Both the accessibility of metals applied to soil as manure co-contaminants and the geographic variability in soil properties were considered.
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