Fertilizer P-derived uranium continues to accumulate at Rothamsted long-term experiments

Sci Total Environ. 2022 May 10:820:153118. doi: 10.1016/j.scitotenv.2022.153118. Epub 2022 Jan 15.

Abstract

The application of phosphorus (P) fertilizers inevitably contributes to the accumulation of trace elements, such as uranium (U), in agricultural soils. The fertilizer-derived U accumulation was first reported in Rothamsted Research in 1979. In the present study, we expand this early key research by evaluating the fertilizer-derived U accumulation in topsoil (0-23 cm) from 1876 to the 2010s. We found that total U accumulation rates ranged from 2.8 to 6.1 μg U kg-1 yr-1 at the Broadbalk and Park Grass, respectively, being similar to those observed 40 years ago. This highlights that U accumulation is still an ongoing process in Rothamsted. Fortunately, the proportion of fertilizer-derived U did not significantly increase in the ammonium acetate extractable ('proxy' of plant-available) fraction over 130 years. In addition, we compiled an overview of the global rate of mineral P fertilizer-derived U accumulation in agricultural systems using existing literature (36 experimental trials, from 11 countries). The resulting dataset predicts an estimated mean U accumulation of 0.85 μg U kg-1 soil for an annual application of 1 kg P ha-1 in the topsoil of agricultural systems (0.26 μg U kg-1 per kg P ha-1 for arable land and 1.34 μg U kg-1 per kg P ha-1 for grassland). The annual U accumulation per applied kg P ha-1 being 0.08 (Broadbalk) and 0.17 μg U (Park Grass) corresponds to around one-third and one-eighth of the worldwide mean U accumulation for their respective agricultural systems, suggesting 'relatively' low U contents of the applied P fertilizers. Our study underscores that fertilizer-derived U accumulation is a persistent problem on the global scale, even if at different rates, and therewith suggests an evaluation of current regulatory limits and acceptable U input levels from P fertilization.

Keywords: Agriculture; Fertilizer-derived uranium; Phosphorus; Rothamsted; Soil.

Publication types

  • Review

MeSH terms

  • Agriculture / methods
  • Fertilizers / analysis
  • Phosphorus
  • Soil
  • Soil Pollutants* / analysis
  • Uranium* / analysis

Substances

  • Fertilizers
  • Soil
  • Soil Pollutants
  • Phosphorus
  • Uranium