Isotope Tracing of Long-Term Cadmium Fluxes in an Agricultural Soil

Abstract

Globally widespread phosphate fertilizer applications have resulted in long-term increases in the concentration of cadmium (Cd) in soils. The accumulation of this biotoxic, and bioaccumulative metal presents problems for the management of soil-plant-animal systems, because the magnitude and direction of removal fluxes (e.g., crop uptake, leaching) have been difficult to estimate. Here, Cd isotopic compositions (δCd) of archived fertilizer and soil samples from a 66 year-long agricultural field trial in Winchmore, New Zealand, were used to constrain the Cd soil mass balance between 1959 and 2015 AD, informing future soil Cd accumulation trajectories. The isotopic partitioning of soil Cd sources in this system was aided by a change in phosphate source rocks in 1998 AD, and a corresponding shift in fertilizer isotope composition. The dominant influence of mixing between isotopically distinct Cd end-members was confirmed by a Bayesian modeling approach. Furthermore, isotope mass balance modeling revealed that Cd removal processes most likely increased in magnitude substantially between 2000 and 2015 AD, implying an increase in Cd bioaccumulation and/or leaching over that interval. Natural-abundance stable isotopes are introduced here as a powerful tool for tracing the fate of Cd in agricultural soils, and potentially the wider environment.

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

“…Furthermore, Cd isotope data for numerous different mineral P fertilizers reveal that the great majority are characterized by d 114/110 Cd values of less than 0.20&. [33][34][35] Use of such fertilizers in the more distant past is thus unlikely to have caused the observed high d 114/110 Cd ¼ 0.24& for the 0-5 cm topsoil at Site A-2 ( Fig. 2 and Table 2).…”

“…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.…”

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

“…Two recent studies reported on the use of stable isotopes at natural abundance to determine the impact of past anthropogenic Cd inputs on the current Cd stocks in soils. Salmanzadeh et al (2017) showed that the Cd stock of arable soils can be dominated by past applications of mineral P fertilizers. This finding is based on distinct isotope ratios of old and new mineral P fertilizers, which governed the Cd isotope compositions in the soils of a long-term field trial in New Zealand.…”

Enmiendas orgánicas en la inmovilización de cadmio en suelos agrícolas contaminados: una revisión

“…En la agricultura, la principal fuente de este metal es la aplicación de fertilizantes que contienen fosfatos, estos hacen que el Cd se acumule en suelos agrícolas y por lo tanto aumente el riesgo de su transferencia a través de la cadena alimentaria (Roberts, 2014;Salmanzadeh et al, 2017). Hoy en día, se necesitan urgentemente técnicas factibles para remediar los suelos contaminados con Cd y con ello; garantizar la inocuidad de los alimentos y proteger la salud pública (Guo et al, 2018a).…”