Trace metal accumulation in agricultural soils from mineral phosphate fertiliser applications in European long‐term field trials

Abstract

Mineral phosphate (P) fertilisers are the main suspected sources of uranium (U) and cadmium (Cd) input to agricultural soils. This study was set up to survey the general long‐term impact of P fertilisers on concentrations of Cd, U and other trace metals in European soils. A total of 218 soil samples was collected from 15 long‐term (3–78 years, median 18 years) P trials at 11 locations with a pairwise comparison of topsoil composition between the fertilised and corresponding unfertilised soils. Aqua regia soil extraction detected the effects of fertilisation more sensitively than the HF (real total) soil extraction. Statistically significant differences in aqua regia soluble metals due to fertiliser application were detected more frequently for U (10 of 15 trials) than for Cd (4 of 15 trials). The concentrations of U and Cd in soil linearly increased with cumulative applied P across all soils and sites; a total addition of 1 ton P ha−1 increased the mean topsoil (23 cm depth) concentrations by 0.11 mg U kg−1 soil (0.09–0.12 mg U kg−1, 95% CI) and 0.03 (0.02–0.04) mg Cd kg−1 soil. These results correspond with mass balance predictions (1 ton P ha−1; +0.15 mg U kg−1 soil and +0.02 mg Cd kg−1 soil) based on previously determined average trace element concentrations in European fertilisers. Data thus suggests that, on average among trials, losses of Cd from soil are undetectable. In contrast, about 30% of the theoretical U input from fertilisers is lost in the same trials. This study provides data to better evaluate the modelled trace metal accumulations in soil and to evaluate the prevailing metal limits in mineral fertilisers. Highlights U and Cd accumulation in agricultural soils correlates with cumulative mineral P‐fertiliser dose. Accumulation of fertiliser‐derived U is more often detectable compared to Cd. Due to its accumulation potential, U accumulation should be monitored. Aqua regia soluble concentrations better detect metal accumulation in soil than real total concentrations.

Uranium Dissemination with Phosphate Fertilizers Globally: A Systematic Review with Focus on East Africa

“…The applications of P fertilizers have been reported to enhance U concentrations in agricultural soils on different continents around the world. For instance, in Asia [15][16][17][18][19][20][21][22][23][24][25][26], similar in Europe [16][17][18][19][20], in Australia [21,22], in America [23][24][25][26], and in Africa [27][28][29][30][31]. This study revealed that from all reviewed articles, the concentration of U from Minjingu P fertilizers from Tanzania ranged from 200 to 600 mg kg −1 , which is similar to what is found in open-pit commercial uranium mines in Namibia.…”

Colloids facilitate transport of cadmium and uranium in arable soils, which is undetected by suction cups in the field

“…The aqua regia U and Cd concentrations in this study are lower for U, not for Cd, than the real total soil concentrations (microwave digestion with HF, HNO 3 and H 2 O 2 ) measured by Bigalke et al (2020) (Table 1). This was expected as aqua regia does not dissolve silicates and thus omits the U bound in the silicate crystal lattice, which is unavailable for leaching processes and plant uptake (Bergen et al, 2021). The NE soil has limestone throughout the soil profile, which is relevant for U as soluble uranyl carbonate complexes can form (Langmuir, 1978).…”

“…The assessment of the annual leaching of Cd in soil at an EU‐wide scale was the most critical part of the Cd regulation (Bergen et al, 2023; Verbeeck et al, 2020) and was open to criticism (Sterckeman et al, 2018), hence calling for more reliable data and models. In contrast to Cd, there is no EU legislation yet for uranium (U) in P fertilizers, even though soil U concentrations change more significantly and more markedly than soil Cd in response to long‐term P fertilization (Bergen et al, 2021).…”

Tracing the Environmental Effects of Mineral Fertilizer Application with Trace Elements and Strontium Isotope Variations

“…Previous studies have shown that PRs are the primary source of trace elements (TEs) incorporated into mineral fertilizer, such as V, Cr, As, Se, Mo, Cd, and U. − Accumulation of some of these elements has been observed in agricultural soils and can be highly variable based on fertilizer utilization and soil chemical properties. ,− Several studies have investigated the Sr isotope ratio ( 87 Sr/ 86 Sr) in PRs, − and one study has shown the similarity between the 87 Sr/ 86 Sr ratio of PRs and mineral fertilizers originating from the same geographical region . Additionally, a few studies have characterized and applied the Sr isotope ratio of fertilizer as a tracer for delineating their environmental impact. ,− However, these studies have investigated the occurrence of TEs and the utility of Sr isotopes only in specific case studies.…”