Heavy Metals Pollution of the Atlantic Marine Environment by the Moroccan Phosphate Industry, as Observed through their Bioaccumulation in Ulva Lactuca

Abstract

The Moroccan phosphate industry releases large amounts of heavy metals in the Atlantic Ocean in the surroundings of two places: Safi and Jorf Lasfar. The major waste, called phosphogypsum and composed of calcium sulphate and other additional salts, is introduced into sea water in particulate form. After dissolution of the particles, heavy metal concentrations can be influenced near the release point. Two multi-element analytical techniques were used to measure 47 element concentrations in various materials involved in the study of the phosphate pollution: Inductively Coupled Plasma Mass Spectrometry (ICPMS) and instrumental neutron activation analysis (INAA). At first, phosphate and phosphogypsum were characterized in order to recognize the overall features of the heavy metal pollution source. From the yearly amount of phosphogypsum produced by the Moroccan industry and the element concentrations in phosphogypsum, it has been possible to estimate a yearly flux of heavy metals introduced in the Atlantic Ocean. Algae were used as bio-accumulator materials of heavy metals in the marine environment, in the region of Jorf Lasfar, in order to significantly reveal the signal of the heavy metal pollution. Ulva lactuca Linnaeus was selected to assess heavy metal pollution around the waste release point. Accumulation factors were determined for 47 elements in U. lactuca, by comparing mean concentrations obtained in algae collected in non-polluted sites (background sites) and an average sea water concentration given in the literature. The ratio between the concentration in U. lactuca, collected in a polluted site to the background concentration in U. lactuca, was determined, giving an estimate of the pollution factor for the same elements by the phosphate industry. The decrease of the pollution due to the dilution in the sea water was observed as far as 6 km southward of the release point. A specific variation was observed for lead and its isotopic composition, denoting that the phosphate industry is not the only pollution source in this region. Natural processes were likely involved to induce the lead concentrations variations along the littoral.