Transects of polycyclic aromatic hydrocarbons and organochlorine pesticides in an urban estuary using passive samplers.

Hydrophobic organic contaminants (HOCs) are tracers of anthropogenic impacts, which can negatively affect water quality. The relative importance of new emissions versus the remobilization of HOCs from legacy reservoirs is not well constrained. Polyethylene passive samplers were deployed in vertical profiles at four sites to determine the concentrations and gradients of atmospheric and freely dissolved polycyclic aromatic hydrocarbons (PAHs) and freely dissolved organochlorinated pesticides (OCPs) in Narragansett Bay, an urban estuary. The concentrations of the sum of 20 PAHs ranged from 4.3 to 240 ng/m3 in the air and 3.2-21 ng/L in the water column, dominated by phenanthrene and pyrene. OCP concentrations varied from below the detection limit to 150 ng/L in the water column. Common OCPs included α-hexachlorocyclohexane, hexachlorobenzene, and aldrin. Gradients displayed net deposition for PAHs, but equilibrium through the water column. Results from this study provided evidence that key OCPs displayed mostly similar concentrations (at or near equilibrium) in the water at both Conimicut Point and Block Island.

Seafloor methane emission on the Makran continental margin.

Seafloor methane emission is widespread on both active and passive continental margins, which may exerts significant impact on global climate change, ocean acidification, cold seep ecosystem, and global carbon cycle. However, due to the limitation of the thick water body, systematic knowledge of detection, quantification and activity of the submarine methane seepage is still unreachable, which greatly limits the assessment of the environmental impact. In 2018, a comprehensive geological survey, including multibeam mapping, seafloor observation, and seismic reflection profiling, was conducted using R/V "Haiyangdizhi 10" on the Makran continental margin. Sixty-five gas flares, which indicated seafloor methane seepage, were detected in a total survey area of 32,000 km2. The total methane flux of the surveyed area is estimated to be 4.7-5.9 × 103 Mg/yr, accounting for 0.013-0.016% of the global seafloor methane emission. In addition, three gas seeps, which were active in 2007, were inactive during our survey in 2018. It is inferred that the intermittent activity might be related to the periodic pressure release and accumulation in the system. All the flares vanish in the water column, which indicates that all the methane gas was oxidized and/or dissolved by seawater. No methane was observed entering the atmosphere in gas phase. In this study, we present new data sets of methane seeps on the Makran continental margin, which are useful to better understand the behavior of the submarine methane seepage.

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.

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.