Influence of Coastal Land Use on Soil Heavy-Metal Contamination in Pattani Bay, Thailand

Expansion of land use in coastal areas results in natural resources being degraded, particularly by soil and water pollution. The objectives of this study were to assess land-use patterns and determine the influence of land-use types on soil heavy-metal contamination in Pattani Bay, Thailand. In studying land use, high-resolution SPOT satellite images were used and analyzed using ArcView GIS 3.2a and ENVI 3.5 software. Collections from 16 soil-sampling sites with topsoil and subsoil layers (0-20 and 21-50 cm in depth) from nine land-use types were carried out during March and April 2006. The heavy metals mercury, lead (Pb), cadmium, arsenic (As), and zinc were analyzed using a Perkin Elmer Optima 2100 DV. Results found that land uses in 2006 were mainly dominated by agricultural, residential, and mangrove-forest areas. In agricultural areas, paddy field were the main land use, followed by shrimp farms. In residential areas, most land was used for living, infrastructure, and industry. Land-use types affected soil pollution in different ways. Municipality areas, industrial zones, and dockyard areas had the highest potential for soil contamination by heavy metals, particularly Pb and As, while shrimp farming and traditional land uses such as salt flats, paddy fields, orchards, and mangrove forests showed low levels of metals. At the dockyard and Pattani River mouth sampling sites, Pb was recorded in high concentrations of 385.77 and 557.15 mg/kg, respectively; the latter exceeds the soil quality standards of the United States Environmental Protection Agency soil screening levels for residential areas (400 mg/kg). A high concentration of As was found at the dockyard, Pattani River mouth, and industrial zone (4.46, 4.75, and 3.48 mg/kg, respectively), while the EPA standard is not to exceed 4.0 mg/kg. The results indicate that using coastal lands without planning and good management negatively influences soil resources degradation, especially in the area of soil pollution.