Distribution of heavy metals in surface sediments of the Bacochibampo Bay, Sonora, Mexico

Abstract

The aim of this study was to determine the levels of heavy metals (Al, Cd, Cr, Cu, Fe, Mn and Pb) in the geochemical fractions of the coastal surface sediments from the Bacochibampo Bay in Sonora, Mexico. Two surveys were conducted (March and September) during 2004, at eight sampling stations inside the bay, and in three natural effluents discharged into this bay. The extraction of metals was carried out using a microwave oven method and the quantification was done by atomic absorption spectrophotometry. The highest detected concentration of total heavy metals in sediments was: Fe4Al4Mn4Pb4Cr4Cu4Cd, with the following concentration values: Fe (1.72%), Al (1.03%), Mn (416.31 mg kg À 1 ), Pb (11.73 mg kg À 1 ), Cr (11.41 mg kg À 1 ), Cu (6.78 mg kg À 1 ) and Cd (1.33 mg kg À 1 ). The levels of total heavy metals (Al, Cr, Cu, Fe, Mn and Pb) were much less than the lowest observable effect level (LEL) which indicates that the sediments were not from polluted areas and that the origin of the metals was due to natural conditions. However, concentrations of Cd were much higher than the low effect level (LEL), over 40% of metal was detected in the exchangeable fraction and carbonates. The normalisation study showed a high degree of enrichment of Cd in all the sampling stations in the Bacochibampo Bay (samples EF 34 -87) and in the natural flows that discharge into this bay (samples EF 22 -35%), which exceeds by several orders of magnitude the value of sample EF 1, which indicates that Cd is anthropogenically induced. Based on these results, it is important that precautionary measures are established, since the deposited Cd in these fractions may be potentially toxic, due to the physicochemical changes that occur in the environment. Thus, future studies will focus on identifying problems involved with Cd bioaccumulation in different trophic levels.

Fractionation and risk assessment of Fe and Mn in surface sediments from coastal sites of Sonora, Mexico (Gulf of California)

“…The contents of carbonates and easily oxidized carbon of the studied sediments were in agreement with previous reports conducted in the same areas (García-Rico et al 2004;Ochoa-Valenzuela et al 2009) and reflect low anthropogenic impact by local activities. The highest levels of carbonates were detected in Guaymas samples (site 4), showing a relatively high calcite content at this site consistent with the abundance of shell fragments of calcareous organisms.…”

“…The total Fe and Mn values were found to be slightly higher than those values (from 0.6 to 1.72 %) reported by Ochoa-Valenzuela et al (2009) in surface sediments from Bacochibampo Bay, located south of Sonora, Mexico, but lower than those levels (from 21,800 to 102,400 mg/kg) reported by Shumilin et al (2011) in surface sediments of the Western Gulf of California. These differences may be due to the natural composition of the sediments, and more importantly, they are related to industrial activities, such as mining and agriculture (Ghrefat et al 2012;Li et al 2011;Ochoa-Valenzuela et al 2009).…”

“…Sediments impacted by Fe may be related with natural flows; a previous report (Ochoa-Valenzuela et al 2009) conducted in Sonora coasts found high levels of Fe (from 2.1 to 4.4 %) and Mn (from 449 to 925 mg/kg, dry wt) in sediments of the effluents discharged into the coast. The National Oceanic and Atmospheric Administration (NOAA) of the USA, in their Screening Quick Reference Tables (SQuiRTs) reported by Buchman (1999) (updated Feb. 2004), presented only values for Apparent Effects Threshold (AET) of 22 % for Fe and 260 mg/kg for Mn.…”

“…These differences may be due to the natural composition of the sediments, and more importantly, they are related to industrial activities, such as mining and agriculture (Ghrefat et al 2012;Li et al 2011;Ochoa-Valenzuela et al 2009). Mn concentrations were similar to those (from 125.36 to 416.31 mg/kg) previously reported by Ochoa-Valenzuela et al (2009) in sediments located in Bacochibampo Bay, Sonora, Mexico, but lower than those values (from 50 to 32,600 mg/kg) reported by Shumilin et al (2011) in surface sediments of the Western Gulf of California.…”

“…Previous works reported anthropogenic impacts on Sonora coastal ecosystems. García-Rico et al (2004) and Ochoa-Valenzuela et al (2009) studied metal distribution in select geochemical fractions of the sediments at the Sonora coasts, and the highest concentrations of non-residual Cd, Cu, and Pb in the Fe and Mn oxide fraction have been found. It has been reported that the metals can form stable complexes with Fe and Mn oxides (Bibi et al 2007;Huerta-Diaz et al 2007;Xiangdong et al 2001).…”