Risk assessment of Ni, Cr, and Si release from alkaline minerals during enhanced weathering

Abstract

<jats:title>Abstract</jats:title><jats:p>Calcium- and magnesium-rich alkaline silicate minerals, when applied to soil, can aid in carbon dioxide sequestration via enhanced weathering. The weathering of these silicate minerals is also associated with the release of heavy metals such as Ni and Cr, depending on the composition of the parent rock, and also labile Si. This paper critically analyses the risk associated with the release of Ni, Cr, and Si from alkaline silicate minerals as a result of enhanced weathering to evaluate its potential to be applied as a soil amendment. Based on the available data in the literature, this study evaluates the soil contamination level and quantifies the risk these elements pose to human health as well as the environment. To assess these potential threat levels, the geoaccumulation index was applied, along with the method recommended by the US Environmental Protection Agency for health risk assessment. The main findings of this study indicate the potential release of Ni, Cr, and Si to exceed the soil quality guideline value. The geochemical index suggests that the analyzed samples are in the class 0–3 and represents sites that lie between uncontaminated zones to highly contaminated zones. The hazard index value for Ni and Cr is greater than unity, which suggests that Ni and Cr release poses a non-carcinogenic risk. The probability of labile Si concentration in the soil to exceed the critical value is found to be 75%.</jats:p>

The Dissolution of Olivine Added to Soil at 4°C: Implications for Enhanced Weathering in Cold Regions

“…One of the key areas of research surrounding the potential of enhanced weathering is the investigation into the build-up of toxic elements in soils and the water column (Renforth, 2012;Hartmann et al, 2013;Renforth et al, 2015;Haque et al, 2020). This potential environmental risk could limit the application of enhanced silicate weathering as a method of carbon sequestration.…”

“…High retention of heavy metals in soils is observed throughout the world in relation to mature soils (Haque et al, 2020), both in secondary minerals (largely clays) and adsorbed. Some laterites have high Ni content (Lewis et al, 2006), with some serpentinite zones showing >2% Ni.…”

“…Further, we have revisited the original experiments, and preconcentrated solutions to better assess the behavior of toxic heavy metals (e.g., Ni, Cr) during the dissolution of olivine. This is in order to determine whether the use of olivine can lead to dangerous accumulations of such metals in either soils or surface waters (Haque et al, 2020).…”

Phytoprevention of Heavy Metal Contamination From Terrestrial Enhanced Weathering: Can Plants Save the Day?

“…In phytoremediation, plants are used to treat soils after they have been contaminated. The existence of these approaches suggests that they could be used preemptively to prevent accumulation and contamination of soils with HM released from TEW (Haque et al, 2020a) -termed "phytoprevention" here. In combination with TEW, this seems a promising approach given that plant species have been identified that (hyper-)accumulate Ni and Cr from soils and waters.…”

Is the climate change mitigation effect of enhanced silicate weathering governed by biological processes?

“…Moreover, positive growth responses can increase C sequestration in plant biomass if silicates are applied in (semi‐)natural ecosystems where biomass can accumulate (Goll et al, 2021). On the contrary, it might be concerning that ESW is accompanied by the release of heavy metals like Ni and Cr (Beerling et al, 2018; Haque, Chiang, et al, 2020; Hartmann et al, 2013). Nonetheless, the application of Ni is not necessarily problematic and below a certain threshold, Ni may even be beneficial for plants (Ahmad et al, 2011; Kumar et al, 2018).…”