Concentration, distribution and sources of perfluoroalkyl substances and organochlorine pesticides in surface sediments of the northern Bering Sea, Chukchi Sea and adjacent Arctic Ocean.

Perfluoroalkyl substances (PFAS) and organochlorine pesticides (OCPs) in surface sediments were investigated from the Bering Sea, the Chukchi Sea and adjacent Arctic Ocean in 2010. Total concentrations (dry weight) of Σ14PFAS in surface sediments (0.85 ±â€¯0.22 ng g-1) of the Bering Sea were lower than that in the Chukchi Sea and adjacent Arctic Ocean (1.27 ±â€¯0.53 ng g-1). Perfluoro-butanoic acid (PFBS) and perfluoro-octanoic acid (PFOA) were the dominant PFAS in these areas. The concentrations of Σ15OCPs in the sediment of the Bering Sea (13.00 ±â€¯6.17 ng g-1) was slightly higher than that in the Chukchi and Arctic Ocean (12.05 ±â€¯2.27 ng g-1). The most abundant OCPs were hexachlorocyclohexane isomers (HCHs) and dichlorodiphenyltrichloroethane (DDT) and its metabolites. The composition patterns of HCHs and DDTs indicated that they were mainly derived from the early residues via river runoff. Increasing trends of PFAS, HCHs and DDTs in surface sediments from the Bering Sea to the Arctic Ocean were found, indicating oceanic transport. In summary, the concentrations of OCPs were orders of magnitude greater than the observed PFAS concentrations, and the concentrations of PFAS and OCPs in surface sediments from the Bering Sea to the Chukchi Sea and adjacent Arctic Ocean are at the low to moderate levels by comparing with other coastal and marine sediments worldwide.

Evaluation of marine sediment contamination by polycyclic aromatic hydrocarbons along the Karachi coast, Pakistan, 11 years after the Tasman Spirit oil spill.

On July 27, 2003, a spill of approximately 31,000 tons of Iranian light crude oil affected the coast of Karachi, Pakistan. Approximately 11 years after the spill, we analyzed polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues (alkyl-PAHs) as the indicators to evaluate the residual effect of oil spill to the sediment along the Karachi coast. The total concentrations (dry weight) of parent PAHs and alkyl-PAHs ranged from 121.9 to 735.4 and 42.3-1149.9 ng/g, respectively. The estuary and harbor were the two regions with the highest levels of PAHs in the sediment. Conversely, sedimentary PAHs in the oil spill areas and remote coastal areas showed significantly lower levels. Although the results of the source identification indicated the up to 75.2% of the contribution from petroleum and its derivatives, this could only reflect the direct impact of the Karachi city on the presence of PAHs in the coastal sedimentary environment and did not indicated that the oil spill continues to stay 11 years later. Compared with 11 years ago, the sharply reduced PAH content, great changed composition, and the degradation driven trend of diagnostic ratios all indicated a sharp decrease in the influence of PAHs caused by the oil spill. Finally, the ecological risk caused by the PAH residual in the marine sedimentary ecosystem had disappeared along the Karachi coasts, Pakistan.

Empirical estimation of suspended solids concentration in the Indus Delta Region using Landsat-7 ETM+ imagery.

Suspended Solids Concentration (SSC) in water is related to its quality and transparency. Satellite remote sensing has proven to be an efficient means of monitoring water quality in large deltas because in situ sampling methods are costly, laborious, time consuming, and spatially constrained. In this study, the potential of Landsat's Enhanced Thematic Mapper Plus (ETM+) sensor was explored to develop a model for remote sensing-based quantification of SSC within the large, turbid Indus Delta Region (IDR, south of Pakistan). Six scenes were atmospherically corrected using the Dark Object Subtraction (DOS) method, to formulate a model for monitoring water quality of the IDR. An empirical model was developed and validated using in situ SSC measurements (9.4-761.4 mg/L) from several data collection campaigns coinciding (within an 11-day window) with satellite overpasses. It was found that using Band 1 (blue: 450-520 nm), Band 2 (green: 520-600 nm), Band 3 (red: 630-690 nm), and Band 5 (shortwave infrared: 1550-1750 nm) of Landsat-7 ETM + along with the Normalized Difference Suspended Sediment Index (NDSSI) can help in precise and accurate estimation of SSC, resulting in a relatively small Root Mean Square Error of 67.24 mg/L, Mean Absolute Error of 54.75 mg/L, and coefficient of determination of 0.88. Further, it was also evident that residuals do not increase with an increasing time window (0-11 days) between the satellite overpass and in situ data collection. Therefore, the established algorithm can potentially be used for frequent (after 8 days) synoptic mapping of SSC in the IDR and other similar estuarine environments.