Pesticide residues in coastal waters affected by rice paddy effluents temporarily stored in a wastewater reservoir in southern Japan.

This paper presents the occurrence, distribution, and environmental impact of pesticide residues in coastal water in southern Japan that receives effluents from a wastewater reservoir temporarily storing surface runoffs of rice paddy fields located near the coastline during the 2005 rice planting season. Concentrations of 14 target pesticides were measured by GC-MS and the hazards posed by the most important pesticides detected were evaluated by acute toxicity tests using a marine diatom, Chaetoceros sp., and a marine amphipod, Hyale barbicornis. Six pesticides (fenobucarb, flutolanil, iprobenfos, mefenacet, phthalide, pyriproxyfen) were detected in the coastal water, with three pesticides (fenobucarb, iprobenfos, and mefenacet) having 100% frequencies of detection. The maximum concentration of mefenacet, at 4.22 microg/L, was at least one magnitude higher than that of fenobucarb and iprobenfos, at 0.27 and 0.19 microg/L, respectively, while the three remaining pesticides had concentrations just around the detection limit of 0.01 microg/L. Consequently, detected concentrations of mefenacet were highly correlated with salinity levels, confirming that the wastewater reservoir is a major source of rice pesticide residues in this particular coastal environment. Hence, the spatial distribution of mefenacet was simulated using their relationship and the results indicate that mefenacet has a tendency to enter and spread to a relatively wide portion of the coastal area during the rice planting season. There is also a possibility that the other pesticides used in rice farming such as fenobucarb and iprobenfos may show similar distribution patterns in coastal waters when they are present in the wastewater reservoir at higher concentrations. These pesticides, however, manifested low acute toxicities to both Chaetoceros sp. and H. barbicornis, suggesting little impact to marine organisms.

Evaluation of the bioremediation potential of mud polychaete Marphysa sp. in aquaculture pond sediments.

Organic enrichment from aquaculture could alter the chemical composition of the fishpond bottom by increasing the levels of organic matter (OM), sulfur (S), iron (Fe), and lower pH of the sediment. Polychaetes can contribute to the nutrient cycling and remediation of polluted sediment. A laboratory experiment was conducted to test the remediation potential of small and large mud polychaete Marphysa sp. introduced to two types of fishpond sediment. Initially, Sediment A had lower OM, S, Fe, and higher pH than Sediment B. After 30 days, in Sediment B, large polychaetes significantly decreased the OM level (27%) while both small and large polychaetes promoted significant decreases of S (71%) and Fe (70-73%) in both sediment types. The increase of sediment pH was promoted by the presence of polychaetes (0.53-0.69) although pH level in small polychaete was not significantly different with the no polychaete treatment. Regardless of polychaete treatment, the pH level of Sediment B (1.04 ± 0.10) was significantly improved than that of Sediment A (0.17 ± 0.02). In both sediments, large polychaetes (95%) had better survival rates than small polychaetes (73%). These findings reveal that large Marphysa sp. can significantly improve sediment quality by decreasing the levels of OM, S, and Fe and improve pH level to a more basic form without compromising its survival. Large polychaetes are recommended to be used as bioremediators of organically enriched aquaculture pond sediment.

Oil spill off the coast of Guimaras Island, Philippines: Distributions and changes of polycyclic aromatic hydrocarbons in shellfish.

The sinking of the Solar 1 tanker caused serious heavy oil pollution around Guimaras Island, Philippines. In the present study, variations of parent polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs (alkPAHs) in some shellfish were investigated around Guimaras Island and other small islands from 3months to 5years after the spill. The total PAHs and alkPAHs in shellfish were detected in high concentrations at 448 and 33,666ng/g dry weight, respectively, in November 2006. The concentrations of alkPAHs gradually decreased, while the parent PAHs in shellfish degraded more slowly than the alkPAHs, which was likely due to the persistent characteristics of PAHs. The risks based on European Union regulations were insignificant in 2008, but total PAHs in shellfish were still over 8 times higher at the investigated sites in November 2011 than that before the oil spill.

Simulated distribution and ecotoxicity-based assessment of chemically-dispersed oil in Tokyo Bay.

To assess risks of chemically-dispersed oil to marine organisms, oil concentrations in the water were simulated using a hypothetical spill accident in Tokyo Bay. Simulated oil concentrations were then compared with the short-term no-observed effect concentration (NOEC), 0.01 mg/L, obtained through toxicity tests using marine diatoms, amphipod and fish. Area of oil concentrations higher than the NOEC were compared with respect to use and non-use of dispersant. Results of the simulation show relatively faster dispersion near the mouth of the bay compared to its inner sections which is basically related to its stronger water currents. Interestingly, in the inner bay, a large area of chemically-dispersed oil has concentrations higher than the NOEC. It seems emulsifying oil by dispersant increases oil concentrations, which could lead to higher toxicity to aquatic organisms. When stronger winds occur, however, the difference in toxic areas between use and non-use of dispersant is quite small.