Japan once faced serious water pollution caused by economic growth, increasing concerns about adverse effects on people and the ecosystem. To improve the water environment, a sewage system was constructed to remove pollutants by focusing on biochemical oxygen demand (BOD), suspended solids (SS), nitrogen, phosphorus and the number of colitis germ legions. This traditional sewage treatment has markedly improved the water quality of rivers and lakes. However, in recent years, chemicals that are physiologically active (act strongly on human body) are found in treated effluent from sewage-treatment plants. The effects of pharmaceutical ingredients in environmental water on the ecosystem are unknown, and there are no regulations on residual amounts nor any laws to prevent contamination. Drug-resistant bacteria have also been detected in rivers inside and outside of Japan, but the actual contaminations have been scarcely surveyed. I am studying this issue so that we can take measures before damage occurs to human health or the ecosystem.
Treated effluent from a sewage-treatment plant is discharged to a river. Sometimes, the purification plant is located downstream of a sewage-treatment plant, resulting in unintentional use of treated effluent as raw water. Wastewater from farmlands and livestock farms may be discharged to a river and be contained in raw water for the water supply (Fig. 1). Environmental pollutants such as heavy metals, pesticides, and dioxins in the environment and drinking water have regulatory values established and are monitored. On the other hand, pharmaceutical ingredients are likely present in wastewater from hospitals, ordinary homes, farmlands and livestock farms, but their effects on the ecosystem have not been fully investigated. There is no legal system for regulating their concentration in water environment (Table 1).
An objective of my study is to develop a simple and inclusive method, which can also be used in the laboratory, for measuring, analyzing and assessing physiological activities of pharmaceutical ingredients in environmental water, for which information for judging the effects on the human body and the ecosystem has been scarce. The TGFα shedding assay is an in vitro assay for measuring pharmaceutical ingredients in environmental water. It can easily detect physiological activities targeting at G protein coupled receptors (GPCR). I was the first person to use the assay to measure physiological activities of GPCR drugs in sewage and river water in Japan. Ingredients of drugs for treating high blood pressure, angina pectoris, allergic rhinitis, etc. were found. Because 1) these drugs also act on the central nervous system and 2) the gene for GPCR is well preserved in the course of evolution and is thus present not only in mammals including humans but also in higher animals such as fish and even in water fleas, the effects of these drugs on behaviors of aquatic organisms are concerning and may be used as a surrogate for the effects of these drugs on humans.
It is necessary to quantitatively investigate which concentrations a pharmaceutical ingredient do not affect human body and the ecosystem, or in other words, above what concentration the drug is dangerous. In order to investigate the effects of pharmaceutical ingredients that are widely prescribed in Japan, such as GPCR drugs and antidepressants, on behaviors of aquatic organisms, I am doing joint investigation with researchers who are analyzing behaviors of fish. We have discovered that antidepressants particularly cause abnormal behaviors at a concentration much lower than the lethal level. I believe that we will be able to determine the residual levels allowed in treated effluent by assessing a large number of GPCR drugs and antidepressants in the joint research and determining their concentrations that do not cause abnormal behaviors (Fig. 2).。
Environmental water has also been found to contain drug-resistant bacteria, which are attributed as a cause of nosocomial infection and new drug resistance genes. Drug-resistant bacteria are physically removed or inactivated (sterilized) together with many other bacteria in the process of sewage treatment. However, the drug-resistant genes may remain inside the inactivated bacterial cell or, even if released outside the cell remains as a viable plasmid. Considering the fact that a certain level of antibiotic inflows constantly into a sewage-treatment plant, there is a possibility that the antibiotics apply selection pressure and that a new drug-resistant bacterium is born by a bacterium incorporating the drug-resistant gene in the process of sewage treatment. Information is also insufficient on the amounts of drug-resistant bacteria and drug resistance genes discharged from a sewage-treatment plant to a river. I thus started a study using a large-scale detection system and a next-generation sequencer in order to precisely analyze the spread of drug-resistant bacteria and drug resistance genes during sewage treatment and in river environments.
Problems related to maintaining human health and the ecosystem should be prevented by taking measures before damage is manifested. The effects of pharmaceutical compounds on water in the ecosystem appear at various levels such as molecular, cellular and organism levels. Therefore, I will cooperate with researchers not only of environmental engineering but also of diverse fields such as biology, fisheries science, molecular biology, pharmacy, and medicine and will accumulate scientific evidence which the administrative and legislative bodies may use in devising countermeasures or regulation.