Heavy Metals Monitoring in Sediments from Lerma River in West-Central Mexico

Abstract

The aim of this work was to carry out monitoring of some elements considered toxic in sediments from Lerma River. An analytical method was optimized in our laboratory for quantification of nickel (Ni), cobalt (Co), manganese (Mn), arsenic (As), chromium (Cr) and lead (Pb) by using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Ten sediments were collected along the Lerma River at variable distances and at 20 cm depth. Samples were heated to 60°C to dryness, followed by separation of particle size using a 74-μ No. 200 mesh for homogeneity purposes. 0.2 g of sample underwent microwave-assisted acid digestion, followed by plate evaporation. The samples were dissolved in 10 mL with HNO3 at 5% v/v for ICP-OES analysis. A certified reference material (CRM 8704) was used to evaluate the method’s accuracy and precision. The method showed linearity, precision, accuracy, and limits of quantification and detection acceptable for protocol validation of analytical method. The average results obtained in recovery of CRM 8704 were ~90% and precision was below 7% for all elements. Levels concentration of As, Cr, Pb show high pollution in A1, A7 and A8 sites. Therefore, Co, Mn and Ni can be considered in this study as normal values. In conclusion, concentration levels of As, Cr, Pb in sediments were high according to US-EPA and NOM-147-SEMARNAT/SSA1-2004. The presence of these heavy metals in Lerma River could be due mainly for the emitted from industries, such as pharmaceutical, automotive, metal mechanics and tannery, and urban residual water. Finally, the method developed using ICP-OES has enabled monitoring of these elements in sediments from Lerma River, with possible applications in a routine analytical laboratory.