Effects of basalt, concrete fines, and steel slag on maize growth and heavy metal accumulation in an enhanced weathering experiment

Abstract. Terrestrial enhanced silicate weathering is a CO2 removal technology involving the application of ground silicate materials to agricultural soils. Next to CO2 sequestration, it can improve soil fertility and crop growth, but silicate materials can also contain toxic trace elements. In a mesocosm experiment, we investigated the effect of basalt, concrete fines and steel slags on biomass, nutrients, and heavy metal concentration of Zea Mays, using a dose-response approach.

Plant biomass increased with basalt, but not with concrete fines and steel slags. Generally, plant Ca, Mg, and corn Si concentrations increased with increasing silicate application amount as a result of increased plant availability. In contrast, plant N, P, and K concentrations were hardly affected by silicate application. Besides increased leaf Pb concentrations with steel slag application, which did not exceed the maximum limit set by the WHO and FAO (0.05 mg Pb kg-1 ww), heavy metal concentrations in aerial plant tissues mostly decreased with increasing silicate application amount, presumably because of an increased soil pH, and accumulation in plant roots. Our study thus indicates mixed effects of silicate application on maize while suggesting that the risk of heavy metal contamination after a one-time application of the tested silicates is limited.