Metal pollution of soils and vegetation in an area with petrochemical industry

Abstract

The aim of this study was to determine the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), manganese (Mn), lead (Pb), and vanadium (V) in soil and chard samples collected in various industrial sites of Tarragona County (Spain), an area with an important number of petrochemical industries. Samples were also collected in urban (Tarragona downtown) and presumably unpolluted (blank samples) sites. Human health risks derived from metal inhalation and ingestion of soils were also assessed. With the exception of an increase in the levels of Cd and V, significant differences in soil samples from the industrial and the unpolluted zone were not found. In chard samples, significant differences between collection sites were only noted for V concentrations. For non-carcinogenic risks, the current levels of metals in the industrial area were lower than those considered as safe for the general population. In relation to carcinogenic risks, only As ingestion and Cr inhalation in the industrial zone might potentially cause an increase of the cases of cancer. A Kohonen self-organized map (an Artificial Neural Network) showed differences in metal concentrations according to the zone of origin of the samples. The current results suggest that although in general terms the petrochemical complex is not a relevant metal pollution source for the area, attention should be paid to As, Cr and V.

Introduction

It is well known that a large number of chemicals involved in petroleum refining and petrochemical manufacturing are toxic in various ways (Mehlman, 1992). Among those, many polyaromatic hydrocarbons, halogenated hydrocarbons, aromatic amines and nitrosamines, and organometallic compounds are mutagens, carcinogens, or both (Kaldor et al., 1984). Some of these toxic substances are released into the atmosphere. Consequently, communities surrounding petroleum and petrochemical plants can be at increased risk of cancer and other adverse health effects (Kaldor et al., 1984, Pan et al., 1994, Bhopal et al., 1998, Lin et al., 2001). Moreover, petrochemical waste contains also inorganic contaminants that can pollute soils and pose ecological and human risks. Therefore, the disposal of petrochemical waste can result in the contamination of soils with Cd, Cr, Cu, Ni, Pb, V and Zn among other potentially toxic elements (Schroder et al., 2000).

Although current environmental levels of metals rarely produce morbidity or death in the general population, the continued exposure to low levels of toxic elements such as As, Cd, Hg, or Pb has been associated with a wide range of adverse effects (Christensen, 1995, Chang, 1996). In addition, some elements are also carcinogenic (Cd, Cr(VI), Ni) and teratogenic (As, Cd, Hg, Pb) in mammals (Domingo, 1994, Chang, 1996). Moreover, although metals such as Co, Cu, Mn, Zn, etc. are essential for humans, they can be also dangerous at high exposure levels (Domingo, 1994, Chang, 1996).

In addition to natural processes, soils can be contaminated by metals released into the environment from a number of anthropogenic sources. These elements can bioaccumulate in plants and animals eventually making their way to humans through the food chain (Frink, 1996, Abrahams, 2002). Ingestion, inhalation and skin contact are the main routes of human exposure to soil metals. Taking into account that soils and vegetation is the major sink for airborne metals, the measurement of metal levels in these media is useful to establish trends in abundance and their consequences as a result of natural and anthropogenic changes.

Since approximately 30 years ago, one of the largest petrochemical complexes in Southern Europe is located in Tarragona County (Catalonia, Spain). A big petroleum refinery, together with a number of important chemical and petrochemical industries are placed in the zone. In recent years, public concern over possible adverse health effects for the population living near this industrial complex has increased. Because of it, we recently initiated a wide survey focused on determining the current levels of various inorganic and organic pollutants in the area, and on establishing the health risks for the population living in the neighborhood of the petrochemical complex. The results concerning metals are presented in this paper. These data are also compared with metal levels from other residential and unpolluted soils of Tarragona County.