Environmental risk assessment of surfactants: Fate and environmental effects in Lake Biwa basin

Abstract

Environmental risk incurred with the use of synthetic surfactants is dealt with in this paper. The background and necessity of risk management related to surfactant usage in the Lake Biwa basin are introduced, as well as a research scheme that acknowledges risks in three sub-processes—consumption and discharge, fate in aquatic environment, and ecotoxicological response of linear alkylbenzene sulfonate (LAS). The ayu ( Plecoglossus altivelis) has been selected as the significant biological target in the basin. Results of a field survey of the behavior of LAS along streams flowing down to the lake are presented. Included are the estimation and verification of an original unit of surfactant consumption per capita per day based on LAS and MBAS concentrations observed in diurnal monitoring. A simulation model representing the flowdown process of LAS dynamically is formulated, with which longitudinal dispersion, settling, and modified biodegradation of LAS are evaluated in the field survey. On the basis of the research scheme described above, ecotoxicological laboratory tests on ayu have been carried out. The special significance of acute and subchronic effects on ayu in various life stages exposed to low concentrations of LAS can be recognized. It has been concluded that the LC 50 of young ayu is not greater than 0.1 ppm under the disadvantageous condition of high temperature or extreme hardness even in normal ranges of environmental indicators. An advanced plan of risk management for surfactant usage is proposed based on methods of elevated risk, comparative risk, risk-benefit, and balanced risk. The occurrence and magnitude of risk phenomena in each subdivided basin adjacent to the lake are identified, taking into consideration features such as (1) the spawning place of ayu and aquafarms, (2) COD and MBAS concentrations and their tolerable levels in current regulation of stream pollution, (3) socioeconomic perspectives including recreational activities and voluntary actions to improve the neighborhood environment, and (4) future preparation of measures for resolving technological risk including sewerage construction. Because LAS concentrations in several rivers exceed the tolerable level of the most delicate life stage of ayu, latent environmental effects can be suggested. It is concluded therefore that it is necessary to establish a water quality goal related to surfactants that takes patterns of water use and conservation of the ecosystem in the local environment into consideration. These judgments are followed by formulation of the “requirement” for environmental management practice for the Lake Biwa administration.