ARSENIC AND HEAVY METAL POLLUTION IN MUDFLAT SEDIMENTS OF SALINAS DE SAN PEDRO, CALIFORNIA, USA

The Salinas de San Pedro develops mainly into a mudflat habitat, which spreads in an enclosed coastal area containing freshwater as well as saltwater saturated sediments, resulting in a rich biodiversity. The purpose of this study was to assess the contamination in lagoon sediments, where it is mainly attributed to street runoff flowing through heavily populated urbanized area like San Pedro, CA and to wastewater discharge from the Cabrillo Marine Aquarium. We also investigated the role of natural hydrogen sulfide gas discharge from nearby fault area.

In all of these cases, the contamination is dispersed through various water channels that carry untreated effluent of various sources ending up into the small manmade Salinas de San Pedro, before being ultimately dispersed into the Pacific Ocean by tidal mixing. In this study, short sediment cores (up to 20 cm deep) from the Salinas de San Pedro mud were used to assess the recent pollutant deposition processes in response to extensive human activity. The cores consisted of alternating layers of clays and silts, with isolated sandy horizons. Analysis of the sediment cores for heavy metals was conducted with Inductively Coupled Plasma Optical Emission spectrometry for 20 sites showing enrichment for some of these metals.

Heavy metal concentrations in surface sediments varied greatly for each metal, with concentration values (mg/g) ranging from 1.05-4.8 (Al); 0.003-0.011 (As); 0.001-0.005 (Cd); 0.02 to 0.82 (Cr); 0.085-0.47 (Cu); 5.98 – 14.22 (Fe); 0.06-0.19 (Mn); 0.03-0.67 (Ni); 0.05-0.38 (Pb); <0.008-0.069 (Se); 0.18-0.63 (Ti); 0.040-0.091 (V) and 0.149-0.336 (Zn). Overall, the concentrations of As, Cd, Cr, Cu, Ni, and Zn was above the Sediment Quality Guidelines from NOAA; Effects Range Low (ERL). The sediment quality guidelines and geoaccumulation indices showed moderately or strongly polluted levels of As and Cd. The As, Cd, and Se retention in the sediments is highly variable and controlled by local processes resulting in a complex diversity of metal speciation.