Ecological risk of alkylphenol and bisphenol A (BPA) has recently been considered to be an emerging concern, especially for benthic organisms due to their relatively high hydrophobicity. The purpose of this study was to clarify their partitioning behavior and estimate their risks to benthic organisms in Kanagawa prefecture.
The obtained volume fraction solids in sediment (Fsolid_sed) ranged from 0.43 m³/m³ to 0.54 m³/m³. The density of solid phase (RHOsolid) ranged from 1,900 kg/m³ to 3,300 kg/m³. The sediment in the upstream of the river had particles with size bigger than the downstream. The pH of water solution obtained by desorption test ranged from 6.6 to 7.5. There was no significant correlation between their physical-chemical properties and sorption behavior.
The measured solid-water partitioning coefficient of the sediments (Kp_(exam)) increased with increasing the amount of ignition loss in sediment solids and a significant correlation was found between them.
The predicted no effect concentration in sediment (PNECsed) of 4tOP, 280 μg/kg-dry was derived from the no observed effect concentration (NOEC) for Chironomus yoshimatsui and the product of uncertainty factors (UFs). PNECsed of 4NP, 210 μg/kg-dry was derived from NOEC for C. yoshimatsui and UFs. PNECsed of BPA, 440 μg/kg-dry was derived from NOEC for Lumbriculus variegatus and UFs.
NOEC of 4tBP to benthic organisms was not obtained. PNECsed_(exam) of 4tBP was calculated from Kp_(exam), the density of solid phase (RHOsolid), Fsolid_sed and PNECwater. PNECsed_(exam) of 4tBP ranged from 33 μg/kg-dry to 810 μg/kgdry.
The results of screening level ecological risk assessment using PNECsed and measured environmental concentration suggest no significant concern of the selected alkylphenols and BPA for benthic organisms in the river sediments of Kanagawa Prefecture.

The proposal on preparation method of acute aquatic ecotoxicity tests (fish acute toxicity test, daphnia immobilization test and algal growth inhibition test) near the aqueous solubility limit (saturation concentration) through the exposure period is expected in these tests for the poorly water-soluble single organic chemicals. The serial dilution method of water soluble fraction (WSF) and the solvent addition method were substituted and improved using 14 of model poorly water-soluble organic chemical substances having more than 99% purity. The improved solvent addition method was performed as follows: Five test concentration groups were set and the maximum and minimum concentration groups were approximately three times and one third of the apparent solubility, respectively. It was confirmed that the improved solvent addition method could maintain near the apparent aqueous solubility limit of chemical during exposure, was effective for test design of the ecotoxicity test for the poorly water soluble chemicals.

Dichlorvos and fenitrothion were detected frequently in rainwater collected at Yokohama Environmental Science Research Institute located in the Isogo ward of Yokohama in 2001 and 2002. Further, some rainwater samples in 2003 had a lethal effect on Daphnia magna after adding minerals. Thus, toxic potency of insecticide in rainwater (wet deposition) was considered to be an important problem for environmental protection. However, there were few studies on the atmospheric dry deposition of organophosphorous insecticides in Japan. Therefore, atmospheric deposition of dichlorvos and fenitrothion were determined by gas chromatograph mass spectrometer (GC/MS). Average atmospheric deposition amount of dichlorvos was 7.0 ng/m²/hr and that of fenitrothion was 6.3 ng/m²/hr. The highest concentration of insecticides in the aqueous solution exposed to air overnight was less than 0.05 μg/L, although the concentraions of dichlorvos and fenitrothion in rainwater sampled on October 1^st, 2014 were more than 0.10. μg/L. The toxic potency of insecticides in aqueous solution exposed to air overnight might be less than that in rainwater sampled on October 1^st, 2014. However, the concentrations of dichlorvos and fenitrothion in the solution exposed to air overnight were not less than PNEC (predicted no-effect of concentration). Therefore the atmospheric deposition of insecticides was considered to be one of important ecological problems for environmental protection as well as wet deposition of them.