Distribution of heavy metals in marine bivalves, fish and coastal sediments in the Gulf and Gulf of Oman

Abstract

An assessment of marine contamination due to heavy metals was made in the Gulf and Gulf of Oman based on marine biota (fish and various bivalves) and coastal sediment collected in Bahrain, Oman, Qatar, and the United Arab Emirates (UAE) during 2000–2001. Sediment metal loadings were generally not remarkable, although hot spots were noted in Bahrain (Cu, Hg, Pb, Zn) and on the east coast of the UAE (As, Co, Cr, Ni). Concentrations of As and Hg were typically low in sediments and the total Hg levels in top predator fish commonly consumed in the region were <0.5 μg g⁻¹ and posed no threat to public health. Very high Cd concentrations (up to 195 μg g⁻¹) in the liver of some fish from southern Oman may result from food-chain bioaccumulation of elevated Cd levels brought into the productive surface waters by upwelling in the region. Very high As concentrations (up to 156 μg g⁻¹) were measured in certain bivalve species from the region. Although not certain, the As is probably derived from natural origins rather than anthropogenic contamination.

Introduction

Pollution studies in the Gulf and Gulf of Oman, collectively known as the ROPME Sea Area (RSA), are extremely important. The Gulf comprises a relatively shallow, semi-enclosed sea with very high evaporation rates and poor flushing characteristics (Sheppard, 1993). As a result, contaminant inputs undergo more limited dilution and slower dispersion than would occur in open marine systems. The ecosystem is relatively fragile, experiencing elevated temperatures, salinity and UV exposure. Many species function close to physiological limits (Sheppard, 1993), and thus, added stress imposed by pollutants is likely to have severe consequences. Maintaining good marine environmental quality is crucial for several socio-economic reasons. The seafood, notably fish and shrimp, is of value for both local consumption and export revenue. Moreover, the region relies heavily upon the sea water itself as a source of fresh water through desalination (Price et al., 1993).

The RSA has experienced several impacts in recent years that have contributed to pollution burdens in the region. The waterways are heavily utilised, especially with respect to oil tanker traffic, with the consequential discharges related to shipping activities. There are some key industrial developments, especially in Bahrain, that act as localised sources of organic and inorganic pollution. Ongoing industrial development in the region, albeit geographically variable, continues to cause concern with respect to marine environmental quality. Unfortunately, the regional database with respect to many metals is not uniform (Fowler, 2002b). Agriculture, mostly located in the northern zone, is expanding in the region, with the threatened increase of emissions of pesticides and other agrochemicals, including metal-based formulations. However, the current database for agrochemical residues in the Gulf is rather limited (Fowler, 2002a), and even more so with respect to the Gulf of Oman.

Superimposed on trends related to changing land uses, there has been the environmental impact of three wars in the past two decades. Considering metals in the marine environment, some initial consequences were described relatively soon after the 1991 Gulf War. Clam samples collected near Kuwait contained higher levels of several metals (Cd, Cu, Ni, Pb, and V) in 1991 compared to 1985 (Kureishy, 1993). Concentrations of oil-related metals, Ni and V, exhibited slightly elevated concentrations along the oil-impacted coastline of Saudi Arabia relative to other locations in the Gulf in 1991 (Fowler et al., 1993). The effects did not extend as far as Qatar, where there was no observable increase in the concentrations of Hg, Cd, Pb, Cu, Co, and Ni in benthic and semi-pelagic marine organisms (Sadiq and McCain, 1993). A post war assessment of several potential contaminants, including metals, was conducted along the coast of United Arab Emirates (Banat et al., 1998). Moreover, the potential long-term effects have continued to be explored. Various tissues of the blue crab, Portunus pelagicus, collected in Kuwait were analyzed to assess the bioaccumulation of several metals associated with petroleum input a decade after the 1991 Gulf War oil spillage (Al-Mohanna and Subrahmanyam, 2001). The concentrations of trace metals in seawater and particulate matter were determined during 1993 and 1994 in order to assess the environmental consequence of the massive oil spill off the Kuwait Coast during the Iraqi invasion (Bu-Olayan et al., 1998). The interpretation of successive war-induced impacts relies on good environmental data based on reliable techniques demonstrating good quality control.

Under the ROPME-IAEA contaminant screening projects, surveys of heavy metals and organic contaminants have taken place in the Gulf and Gulf of Oman since the early 1980s (Burns et al., 1982; Fowler, 1988; Fowler et al., 1984). Such pre-war studies have proved invaluable for the identification of pollution hot spots and assessing the consequences of the 1991 Gulf War (Fowler et al., 1993). This paper firstly evaluates marine pollution of metals in the coastal zone of the eastern Gulf and Gulf of Oman based on sediment quality. Sediment samples were collected from several coastal locations in Bahrain, Oman, Qatar, and the UAE during 2000–2001. A wide range of elements was determined for pollution assessment and to facilitate interpretation of the origins of potential contaminants. Secondly, the paper examines the quality of local seafood with respect to metal contamination. The focus was on two fish species of commercial importance, namely the orange spotted grouper (Epinephelus coioides, known locally as hamoor) and the spangled emperor (Lethrinus nebulosus, known locally as sha'ri, shaeri or sheiry), together with various bivalves, notably oysters. Overall, the results for sediments and biota contribute to the regional database for the RSA, most notably for Oman given the paucity of such information. Concurrent studies of organotin compounds have been presented elsewhere (de Mora et al., 2003) and similar assessments are under preparation for petroleum hydrocarbons and organochlorinated compounds.