Effects of basalt, concrete fines, and steel slag on maize growth and toxic trace element 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 its CO2 removal potential, 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 slag on biomass, nutrients, and the toxic trace element concentration of Zea mays, using a dose–response approach. Plant biomass increased with basalt but not with concrete fines or steel slag. Generally, plant Ca, Mg, and corn Si concentrations increased with an increasing silicate application amount as a result of increased availability to plants. 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 World Health Organization (WHO) and Food and Agriculture Organization (FAO) (0.05 mg Pb kg−1 ww, where “ww” denotes wet weight), the toxic trace element concentrations in aerial plant tissues mostly decreased with increasing silicate application amount, presumably because of an increased soil pH and accumulation in plant roots. Thus, our study indicates mixed effects of silicate application on maize while also suggesting that the risk of toxic trace element contamination after a one-time application of the tested silicates is limited.