Analysis of Heavy Metals in Sediments from Northern Moroccan Coast Using Simple and Low-Cost Methodology

A new simple and low-cost digestion method for sediment samples was studied and optimized. It was based on the acid digestions of samples into low-pressure PTFE bombs and heating in a simple convection-based oven, as an alternative to available standard methods based on high-pressure bombs and microwave ovens. Although there is no doubt about the benefits of microwave-based methodologies, there is still a problem related with the high cost of the equipment required, making difficult its practical application in some developing countries. The proposed methodology was optimized by using three certified reference materials (CRMs): marine sediment (GBW07313), estuarine sediment (SRM1646a) and river sediment (CRM320), which were digested separately by the two studied methods. Metal concentrations in the digested extracts were analyzed and compared. Average metals recoveries obtained with the new method ranged from 61 \% (Al) to 100 \% (Cd, Co, Pb), and, in general, significant differences between the two methodologies were not observed. The new digestion method was applied to the simultaneous determination of up to ten heavy metals in marine sediments from the Northern Moroccan coastline, in the Mediterranean province of Tetouan and Chefchaouen. The results obtained ranged from 1.26-3.32 \% for Al, 16.2-20.7 mg/kg for Co, 49.7-72.7 mg/kg for Cr, 20.2-32.3 mg/kg for Cu, 2.98-3.92 \% for Fe, 184-394 for Mn, 34.5-44.3 mg/kg for Ni, 36.0-49.7 mg/kg for Pb, 0.46-0.55 \% for Ti, and 67.5-83.6 mg/kg for Zn. A statistical data analysis was performed in order to determine the sources of heavy metals in this area. Relatively high concentrations of Cr, Ni and Pb were measured in all the sampling sites, although their anthropogenic origin could not be established. In addition, Cu and organic matter were enriched in sediments close to agricultural areas.