Miki Sudo

Concentration and loading of pesticide residues in Lake Biwa basin (Japan).

The concentrations and loading rates of pesticides used in paddy fields were investigated over a period of 5 years in the Seta River, which is the only natural outlet of Lake Biwa. The lakes water catchment area is 3,174 km2, 20% of which contains paddy fields. Water samples were also collected in six rivers flowing into the lake in order to compare the contamination level and concentration profile. The pesticides analyzed were four herbicides (molinate, simetryn, oxadiazon, and thiobencarb), one fungicide (isoprothiolane), and two insecticides (diazinon and fenitrothion). Molinate, simetryn, oxadiazon and isoprothiolane were found at the higher frequencies with maximum concentrations of 1.1, 0.4, 0.1 and 0.5 microg,/l in the effluent river, one or two order of magnitude higher than that of effluent in influent rivers. These peak concentrations were observed during the application period in influent rivers and two or three weeks after that in effluent river. The frequency of occurrence of thiobencarb, diazinon, and fenitrothion was relatively low and their maximum concentrations in the effluent remained below 0.1 microg/l. The decrease of molinate, simetryn and oxadiazon concentrations in the effluent river were approximated by two straight lines plotted on semilogarithmic scale. Increased loading was induced by intense rainfall, which took place during the application period. Simetryn and isoprothiolane persisted in relatively high concentrations through the year were also influenced on its loading by the heavy rainfall in the following months. The percentages of the total amount of pesticides released through Lake Biwa to the basin in downstream were estimated to be 1.3-2.9% for molinate, 5.4-10.0% for simetryn, 0.6-1.3% for oxadiazon, 0.2-0.9% for thiobencarb, 1.8-6.6% for isoprothiolane, 0.3-2.1% for diazinon. and 0% for fenitrothion.

Algal growth inhibition by river water pollutants in the agricultural area around Lake Biwa, Japan.

An ecotoxicological study of river water discharged from the agricultural area around Lake Biwa was performed by using algal bioassays to guide chemical analysis. Water samples were collected once a week, at least, for 1 year starting in April 1997 and continuing until April 1998. The toxicities of the dissolved and particulate-adsorbed extracts of water samples were evaluated by the algal growth inhibition test and concentrations of individual pesticides were determined. Most of the river water that was collected during the periods when pesticides were applied to the paddy fields caused algal growth inhibition. Some extracts were found to contain herbicides (molinate, mefenacet, simetryn, or esprocarb) as major compounds. According to chemical assay and bioassay, simetryn was identified as the most toxic compound that caused algal growth inhibition.

Spatial distribution and seasonal changes of pesticides in Lake Biwa, Japan

The spatial distribution and seasonal variation in the concentrations in Lake Biwa of pesticides used in paddy fields were studied. Lake Biwa is the largest lake in Japan and is a recognized water resource for 14 million people in the Kinki district. Samples were collected nine times from April to December 2001 at ten sites within the lake and at the mouths of six influent rivers. Weekly sampling was also carried out at a single site on an effluent river. Among the 20 pesticides analyzed, the detection frequencies in surface water were almost 100% for simetryn, bromobutide, and isoprothiolane; around 75% for molinate and pyroquilon; around 30% for three herbicides and one fungicide; and almost zero for the remaining substances. The maximum concentrations of pesticides detected frequently in the lake were in the range 0.1–0.4 µg l−1. The occurrence of a few pesticides below the thermocline may be explained by thermal stratification and vertical circulation. Although the thermocline suppressed vertical diffusion in spring and summer during pesticide application periods, a few pesticides remaining at the surface of the lake in winter were transported to the hypolimnion by vertical circulation and remained there even after the reestablishment of the thermocline. The half-lives of pesticides in the lake were estimated to be more than a year for simetryn, half a year for bromobutide, 1.5 months for molinate, and 1 month for dimepiperate. The main cause of elimination for molinate and dimepiperate was estimated to be degradation, that for simetryn was outflow, and for bromobutide both degradation and outflow were significant.

Paddy herbicide inputs in the entire river inflow reaching Lake Biwa, Japan

This study estimated the inputs of four paddy herbicides in the entire river inflow reaching Lake Biwa, the largest lake in Japan, which serves as a water resource for 14 million people. The Uso River and the Hino River, the main contaminated rivers among the inflow rivers, were selected as daily and hourly monitoring sites to provide data on the seasonal trends in the concentration and load of herbicides and to determine the effect of rainfall events on load. The monitoring was also performed four times in 15 inflow rivers. The total input to the lake was calculated from the loads during fine weather conditions and additional loads during rainfall events. The former based on the lumped load from the two rivers and by prorating for the 15 rivers, and the latter was estimated from the relation between precipitation and increased load rate. The annual losses of herbicide from the basin to Lake Biwa were estimated to be 14.5% for bromobutide, 3.0% for pretilachlor, 5.2% for molinate, and 8.8% for simetryn. The loads caused by rainfall events accounted for 9%–18% of the total annual loads.

Loading rates of nutrients discharging from a golf course and a neighboring forested basin

In the last ten years, the number of golf courses has been increasing in some countries as the game gains popularity. This indicates, a need to estimate the nutrient loading from golf courses in order to prevent the eutrophication of water bodies. Nutrient concentrations and flow rates of a brook were measured once a week from 1989 to 1990 at two sites: Site A of a brook flowing out from D-golf course (53 ha) and Site B of the same brook discharging into the golf course from an upper forested basin (23 ha) covered mainly with planted Japanese cypress ( Chamaecyparis obtusa SIEB. et ZUCC). The bedrock of the area was granite. The annual values of precipitation and mean temperature were 1947 mm and 13.5°C in 1989, respectively. The arithmetic average values of discharge from the forested basin and the golf course were 0.392 and 1.26 mg/l total nitrogen (TN), 0.0072 and 0.145 mg/l total phosphorus (TP), 0.82 and 3.53 mg/l potassium ion (K + , 5.92 and 8.24 mg/l sodium ion (Na + ), 2.1 and 9.9 mg/l suspending solid (0.001–2.0 mm, SS), 0.087 and 0.147 mS/cm electric conductivity (EC), and 0.031 and 0.037 m 3 /km 2 •s specific discharge, respectively. The loading rates of the forested basin and the golf course were 5.42 and 13.5 TN, 0.133 and 3.04 TP, 8.84 and 33.9 K + , 55.0 and 73.0 Na + , and 54.3 and 118 SS in kg/ha•y. The leaching and runoff rate of nitrogen in the chemical fertilizers applied on the golf course was calculated as 32%. These results indicated the importance of controlling the phosphorus loading for the management of golf courses.

Distribution and pollutant load of hexabromocyclododecane (HBCD) in sewage treatment plants and water from Japanese Rivers

Hexabromocyclododecane diastereoisomers (α-, β-, γ-, δ-, and ε-HBCD) were investigated in river water, sewage influent, and sewage effluent from the Yodo River basin, Japan. The mean annual values of HBCDs ranged from 0.19 to 14ngL(-1) in river water. We observed that the concentrations of HBCDs in the brackish water area were low compared with that in the fresh water area. It was implied that, when the flow of the river stagnated in the estuarine area, HBCDs settled with suspended matter because of their hydrophobic character. In the sewage treatment plants, HBCDs ranged from 16 to 400ngL(-1) in sewage influent, whereas they ranged from 0.39 to 12ngL(-1) in sewage effluent. Over 90% of HBCDs were removed from the wastewater in the sewage treatment plants. By using these results, we estimated the pollutant load of HBCDs that flows into Osaka Bay from the study area. It was estimated that approximately 15kg of HBCDs flow into Osaka Bay from the study area in a year. This value is five orders of magnitude lower than the 2010 market demand for HBCDs (3019 metrictons) in Japan.

Comparison of the Effects of Di(2-ethylhexyl)phthalate, a Peroxisome Proliferator, on the Vitamin Metabolism Involved in the Energy Formation in Rats Fed with a Casein or Gluten Diet

In order to find an alleviation method for the adverse effect of environmental endocrine disrupters, we studied the effects of the putative endocrine disrupter and peroxisome proliferator, di(2-ethylhexyl)phthalate (DEHP), on animal growth and vitamin metabolism. It is known that the effects of chemical compounds such as xenobiotics differ according to the dietary protein source. We compared the effects of dietary DEHP administration on rats fed with a diet containing milk casein or wheat gluten. The increased conversion ratio of tryptophan to nicotinamide by DEHP administration was significantly higher in the casein group than in the gluten group. We also investigated the effects of DEHP on the urinary excretion of other vitamins. DEHP administration resulted in decreased urinary excretion of vitamin B1, vitamin B2, and pantothenic acid.

A Bayesian approach for estimating hexabromocyclododecane (HBCD) diastereomer compositions in water using data below limit of quantification

We developed a statistical model that quantitatively incorporated the stochastic fluctuations of values, which were estimated as Bayesian credible intervals (BCIs), to analyze environmental monitoring data. We used α-hexabromocyclododecane (α-HBCD) diastereomer compositions of water samples that included data points below limit of quantification. To avoid replacing “not detected (ND)” values with irrelevant values in data analysis, we substituted ND with observed values from the measurement system upon examination of the model. In our study, it was assumed that the magnitude of stochastic fluctuations of observed values in environmental samples was identical to that in iterative measurements of a standard solution at the lowest concentration. Using this model, α-HBCD diastereomer compositions could be estimated along with BCIs even for samples collected from sites where concentrations of α-HBCD were ND or near limit of quantification. The brackish areas in our study showed relatively wide ranges in composition for the 95% BCIs compared with samples from fresh water areas. In the brackish areas, concentrations of HBCD were frequently ND or near limit of quantification. Using this model, it was unnecessary to replace ND with zero or limit of quantification in data analysis, and an environmental assessment could be achieved using all of the data. Therefore, this model is considered to be a widely applicable approach in the analysis of environmental monitoring data including ND.