Abstract

Several studies have reported the presence of smithsonite (ZnCO3) in soils polluted by zinc mining. The present study aimed to determine upper critical threshold values of Zn phytotoxicity in a substrate spiked with ZnCO(3)and to compare them with those obtained in field-collected soils. We studied Zn toxicity to perennial ryegrass (Lolium perenneL.) grown in pots with unpolluted peat treated with increasing concentrations of ZnCO(3)that produced nominal total Zn concentrations of 0, 0.7, 1.3, 2.0, 2.6, and 3.3%. To keep constant near-neutral pH value in all the treatments, we used decreasing concentrations of dolomitic lime. In the treatment with total soil Zn of 3.3% (pH 6.8), the foliar Zn concentration ofL. perennewas 1914 +/- 211 mg kg(-1), falling into the range of 2400 +/- 300 mg kg(-1)reported forLoliumspecies grown under similar laboratory conditions in a polluted soil (total soil Zn 5.4%, pH 7.3) collected near a Zn smelter. The value of 92 +/- 98 mg kg(-1)was obtained for the median effective concentration (EC50) values of 0.01 M KNO3-extractable Zn using the responses of shoot dry biomass, shoot length, and total pigments. This value falls within the range of 95 +/- 46 mg kg(-1)reported in other studies for the EC50 values of salt-extractable Zn using field-collected soils. The application of ZnCO(3)for spiking was able to mimic foliar Zn concentrations ofLoliumspecies observed in field-collected soils. The effective concentrations of soil Zn obtained in the present study are comparable to those obtained in field-collected soils. Future research should determine effective concentrations of metals using soils spiked with metal-containing compounds that mimic a real source of contamination.Environ Toxicol Chem2020;00:1-7. (c) 2020 SETAC