Distribution of heavy metals in crop soils from an agricultural region of the Yucatan Peninsula and biochemical changes in earthworm Eisenia foetida exposed experimentally.

Abstract

Heavy metals (HM) are natural components of agricultural soils. However, excessive use of agrochemicals (fertilizers and pesticides) can increase the concentration of these elements, making them harmful to crops and soil biota. Therefore, this study aimed to evaluate the concentrations of 6 HM (Cr, Mn, Cu, Zn, Al, and Fe) in soils collected from a typical agricultural region of the Yucatan Peninsula, Mexico, and relate their effects on weight, biotransformation (EROD, GST), and oxidative stress (SOD, CAT, LPO, and MT) in the earthworm Eisenia foetida. The results showed different concentrations of HM accumulation in soils, in the following order, Fe (598.74 ± 223.81μgg-1), Al (145.30 ± 33.54μgg-1), Cr (88.38 ± 36.23μgg-1), Mn (69.53 ± 22.48μgg-1), Zn (54.10 ± 12.04μgg-1), and Cu (24.91 ± 12.40μgg-1), the soils with maize, soybean, and chihua squash crops being the ones with the highest distribution and availability of these elements. These concentrations of metals did not produce mortality. However, Cr, Fe, and Al induced a significant biomass loss of E. foetida. The integrated biomarker response version 2 revealed that soil with maize cultivation was affected the most, with the earthworms exposed to this soil showing greater variations in the dominant biological responses including EROD, TBARS, SOD, and MT (IBRv2 = 9.73). PCA analysis indicated a strong positive relationship between these oxidative stress biomarkers and Cu and Zn concentrations. These findings provide a reference guide that should be part of the monitoring and management programs for different agricultural types in the region under study.