Assessments of chromium pollution in surface sediment of the inner Gulf of Thailand

Abstract

The inner Gulf of Thailand is an important marine resource for economic and social developments of Thailand. Moreover, the inner Gulf of Thailand is a diverse of biological coastal ecosystem, which is make an equilibrium marine environment. On the other hand, this area is due mainly to a variety of pollutant sources from the surface runoff, particularly major large rivers including the Mae Klong, the Tha Chin, the Chao Phraya and the Bangpakong Rivers. As a result, chromium contamination can occur in the inner Gulf of Thailand and ultimately become a serious environmental issue in Thailand. Therefore, the surface sediments were collected from 58−60 stations entire the inner Gulf of Thailand in southwest monsoon season, northeast monsoon season, and dry season were also affected in the chromium accumulation in the surface sediment of the inner Gulf of Thailand in order to investigate spatial heterogeneity distributions and seasonal changes of total chromium contamination, to analyze geochemical fractions of chromium and to assess the contamination status and ecological risk of chromium. The results revealed that the concentration of chromium in surface sediment in southwest monsoon season, northeast monsoon season, and dry season in the range of 11.72−80.16 mg/kg, 5.61−107.45 mg/kg and 8.63−119.47 mg/kg, chromium contamination in surface sediment was decreased from the river estuaries to the lower of the inner Gulf of Thailand. Fractional distribution of Cr was mostly bound to organic matter and residual fraction. As a result, fraction includes the rest of the metals and is associated with minerals that are bound via their crystalline structure, immobilized, and that will not constitute a threat to the ecosystem. Based on the SQGs, the most of areas may not cause any adverse biological effects, but some areas were occasionally associated with adverse biological effect within the inner Gulf of Thailand. Considering calculation of the enrichment factor (EF) and geo−accumulation index (Igeo) for chromium, indicated that the inner Gulf of Thailand was mostly minor enrichment and practically uncontaminated, respectively. Furthermore, the Er of all stations was less than 40, which was indicated that in the inner Gulf of Thailand is not associated ecological risk. However, the concentrations of exchangeable and carbonate−bound chromium fractions were assessed the ecological risk, which were indicated that the risk level was increased, particularly at almost moderate risk in the dry season. As a result, the Cr concentrations were at low contamination and risk in the surface sediment of the inner Gulf of Thailand, however some area should be concerned, and long−term monitoring is needs to be investigated and assessed the concentration changes over the time.