Using isotopes to trace freshly applied cadmium through mineral phosphorus fertilization in soil-fertilizer-plant systems

Abstract

Applications of mineral phosphorus (P) fertilizer can lead to cadmium (Cd) accumulation in soils and can increase Cd concentrations in edible crop parts. To determine the fate of freshly applied Cd, a Cd source tracing experiment was conducted in three soil-fertilizer-wheat systems by using a mineral P fertilizer labeled with the radio isotope Cd and by exploiting natural differences in Cd stable isotope compositions (δCd). Source tracing with stable isotopes overestimated the proportion of Cd in plants derived from the P fertilizer, because the isotope ratios of the sources were not sufficiently distinct from those of the soils. Despite indistinguishable extractable Cd pools between control and treatments, the addition of P fertilizer resulted in a more negative apparent isotope fractionation between soil and wheat. Overall, the radio isotope approach provided more robust results and revealed that 6.5 to 15% of the Cd in the shoot derived from the fertilizer. From the introduced Cd, a maximum of 2.2% reached the wheat shoots, whilst 97.8% remained in the roots and soils. The low recoveries of the fertilizer derived Cd suggest that continuous P fertilizer application in the past decades can lead to a build-up of a residual Cd pool in soils.

Cadmium isotope fractionation in the soil – cacao systems of Ecuador: a pilot field study

“…Such studies have already shown, however, that coupled Cd concentration and isotope data can be used to trace the origin of isotopically distinct Cd inputs, such as mineral P fertilizers, into soils. [31][32][33][34][35] In addition, isotope data can provide constraints on the distinct cellular and molecular processes that are employed by plants for the uptake, internal transport and sequestration of Cd. In particular, recent publications demonstrated that wheat and barley display similar trends of Cd isotope fractionation 33 and these differ signicantly from the isotope systematics observed for Cdtolerant and accumulator cultivars.…”

The Use of Q-ICPMS to Apply Enriched Zinc Stable Isotope Source Tracing for Organic Fertilizers

“…The radioisotope 65 Zn has successfully been used in soil–plant systems with both source tracing approaches (Sinaj et al, 1999; Diesing et al, 2008; Aghili et al, 2014; McBeath and McLaughlin, 2014; Hippler et al, 2015). Compared to stable isotope systems, radioisotope systems are more readily analyzed (Stürup et al, 2008; Wiggenhauser et al, 2018). However, 65 Zn is a gamma-emitter with a half-life of 244.4 days and safety issues, legal regulation limits for in-situ experiments, transport as well as waste management and storage are problematic and complicate experiments.…”

“…Analysis of such natural variations has allowed source tracing of metals on field or catchment scales (Borrok et al, 2009; Bigalke et al, 2010; Imseng et al, 2019; Yang et al, 2019). However, this approach requires that the isotope ratios of sources and sinks are distinguishable, which is not always the case (Wiggenhauser et al, 2018).…”

δ114/110Cd Values of a Suite of Different Reference Materials

“…2015), assessing the migration of Cd in plants (Wiggenhauser et al . 2016, 2019, Imseng et al . 2018), evaluating Cd containment level in coastal environments (Shiel et al .…”