Trace element concentrations in mineral phosphate fertilizers used in Europe: A balanced survey.

Mineral phosphate (P) fertilizers contain trace elements (TE) and can be a long-term source of these elements in soil. This study aimed to survey TE concentrations in mineral P fertilizers consumed in 25 of the EU-28 countries plus Norway (EU-28+1), to improve estimates of the EU wide input of TEs in agricultural soils. Different mineral P fertilizers (n = 414) were collected from EU-28+1 with a consumption-balanced sampling strategy. The samples were analyzed by ICP-MS for 21 elements (Na, Mg, Al, P, S, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Pb, Sb and U) that had adequate analytical quality control. Trace element concentrations in the P fertilizers were positively correlated with the P content for Cd, U, V, Sb, Cr, As and Ni. In addition, two groups of rock phosphates are likely the basis of P fertilizers in EU-28+1, i.e., with a high TE/P (n = 288) and low TE/P ratio (n = 126). The TE concentrations, relative to the aqua regia soluble concentration in EU arable soils, were highest for U, followed by Cd and then by other TEs. The Cd and U concentrations showed strong association but suggest that rock phosphates with two different Cd/U ratio are used. The Cd/P2O5 ratio varied significantly among countries and averaged 28 mg Cd kg-1 P2O5. An EU weighted mean is 30 mg Cd kg-1 P2O5, based on country average data and P consumption. Both means are below earlier EU estimates, likely because of sampling bias in those surveys. About 10% of the fertilizers exceed the current European Cd limit (60 mg Cd kg-1 P2O5). This survey illustrates the importance of a consumption-balanced sampling strategy to estimate TE inputs at a large scale and provides the data necessary for risk assessment of TEs in agricultural soils.

Oxidation of iron causes removal of phosphorus and arsenic from streamwater in groundwater-fed lowland catchments.

The fate of iron (Fe) may affect that of phosphorus (P) and arsenic (As) in natural waters. This study addresses the removal of Fe, P, and As from streams in lowland catchments fed by reduced, Fe-rich groundwater (average: 20 mg Fe L(-1)). The concentrations of dissolved Fe (<0.45 µm) in streams gradually decrease with increasing hydraulic residence time (travel time) of the water in the catchment. The removal of Fe from streamwater is governed by chemical reactions and hydrological processes: the oxidation of ferrous iron (Fe(II)) and the subsequent formation of particulate Fe oxyhydroxides proceeds as the water flows through the catchment into increasingly larger streams. The Fe removal exhibits first-order kinetics with a mean half-life of 12 h, a value in line with predictions by a kinetic model for Fe(II) oxidation. The Fe concentrations in streams vary seasonally: they are higher in winter than in summer, due to shorter hydraulic residence time and lower temperature in winter. The removal of P and As is much faster than that of Fe. The average concentrations of P and As in streams (42 µg P L(-1) and 1.4 µg As L(-1)) are 1 order of magnitude below those in groundwater (393 µg P L(-1) and 17 µg As L(-1)). This removal is attributed to fast sequestration by oxidizing Fe when the water enters oxic environments, possibly by adsorption on Fe oxyhydroxides or by formation of ferric phosphates. The average P and As concentrations in groundwater largely exceed local environmental limits for freshwater (140 µg P L(-1) and 3 µg As L(-1)), but in streams, they are below these limits. Naturally occurring Fe in groundwater may alleviate the environmental risk associated with P and As in the receiving streams.

Copper toxicity in soils under established vineyards in Europe: a survey.

Copper (Cu) containing fungicides have been used for more than one century in Europe on agricultural soils, such as vineyard soils. Total Cu concentrations in such soils can exceed toxicological limits that are commonly derived using artificially spiked soils. This study surveyed Cu toxicity in vineyard soils with reference to soils spiked with CuCl(2). Soil was collected in six established European vineyards. At each site, samples representing a Cu concentration gradient were collected. A control (uncontaminated) soil sampled nearby the vineyard was spiked with CuCl(2). Toxicity was tested using standard ecotoxicity tests: two plant assays (Lycopersicon esculentum Miller (tomato) and Hordeum vulgare L. (barley) growth), one microbial assay (nitrification) and one invertebrate assay (Enchytraeus albidus reproduction). Maximal total Cu concentrations in the vineyard sites ranged 435-690 mg Cu kg(-1), well above the local background (23-105 mg Cu kg(-1)). Toxicity in spiked soils (50% inhibition) was observed at added soil Cu concentrations from 190 to 1039 mg Cu kg(-1) (mean 540 mg Cu kg(-1)) depending on the assay and the site. In contrast, significant adverse effects were only found for three bioassays in vineyard samples of one site and for two bioassays in another site. Biological responses in these cases were more importantly explained by other soil properties than soil Cu. Overall, no Cu toxicity to plants, microbial processes and invertebrates was observed in vineyard soil samples at Cu concentrations well above European Union limits protecting the soil ecosystem.