Living organisms have several mechanisms of detoxification of xenobiotics for their self-protection. The genera] pathways of biotransformation follow the conversion of lipophilic xenobiotics into more hydrophilic metabolites. Cytochrome P450 (CYP) and glutathione S-transferase (GST) are important families of enzymes involved in the biotransformation of xenobiotics. A number of environmental pollutants are known as inducers of CYP and GST experssion levels. Therefore, the induction phenomenon of metabolizing enzymes in organisms by xenobiotics may be useful as a biomarker for monitoring the levels of environmental pollution. I n this paper, I reviewed the suitability of xenobiotic-metabolising enzymes in aquatic animals as biomarkers of the level of water pollution.

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Cytochrome P450 (CYP) multiple enzyme system plays a major role in oxidative metabolism of a broad variety of endogenous and exogenous compounds, including sterols, fatty acids, drugs and xenobiotics. Some CYP isozymes are known to be induced by xenobiotics, including environmental pollutants. In order to estimate the suitability of using CYP as indicator of environment, we have been investigated about the CYP-dependent activities in hepatic microsomes of feral rodent (Clethrionomys rufocanus) and marine mammal (Phoca largha). From the results of our investigations, it can be concluded that the CYP-dependent activities are useful biomarkers of environmental pollution.

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Metallothionein is a cysteine-rich low molecular weight protein with a high affinity for metals such as cadmium, zinc, copper and mercury, and is induced by these metals and many other factors such as glucocorticoids and cytokines. Metallothionein has been found in a variety of organisms ranging from prokaryotes, eukaryotic microorganisms, plants, invertebrates to vertebrates (fishes, amphibians, reptiles, birds and mammals). Quite a few research groups reported metallothionein as a biochemical marker which reflect exposed level and effects of heavy metals. Induced amounts of metallothionein by exposure to heavy metals such as cadmium and mercury have been reported in human, harbor seal, seabirds, snail, earthworm and fish. Significant correlation between metallothionein levels and cadmium concentrations or exposure doses of cadmium have been established in harbor seal, seabirds, snail, earthworm and several kinds of fish. In people living in cadmium-polluted areas or those occupationally exposed to this metal, the elevated amounts of metallothionein excreted into urine were found to be more sensitive and specific marker than urinary cadmium for renal dysfunction found in these human populations. Metallothionein mRNA level has been also increased by exposure to cadmium or mercury in the blood of human or the liver of fish, respectively, Recently, hepatic metallothionein has been induced by glucocorticoid or violent air-pumping stress in fish. In conclusion, metallothionein is a very useful biomarker for monitoring heavy metal pollution in man and the wild-life.

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A number of chemical compounds have physiological effects indicating they possess estrogenic activity. These xenobiotic estrogens can have harmful effects on wildlife and human health by disrupting reproductive and developmental processes. Recently it was reported that caged male rainbow trout placed in the effluent of sewage-treatment works, were induced to synthesize vitellogenin. Vitellogenin is a protein that specifically appears in blood of sexually maturing female oviparous animals. Vitellogenin is a glycolipophosphoprotein that is produced by the liver in response to circulating estrogen, released into the blood stream, taken up by the developing oocytes, and chemically modified in the process of yolk formation. Vitellogenin is normally found only in the blood of adult females, but it can be induced in males and immature females by estrogen. The presence of vitellogenin in the blood of male fish can be used as a biomarker for estrogenic contamination of the aquatic environment.

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Endocrine disrupting chemicals impair the reproductive systems in wildlife. It has been hypothesized that endocrine disrupting chemicals may play a role in the decrease in the quantity of human semen during the last 50 years. However, linking the decline in sperm density to environmental factors may be premature. It is necessary to develop bioassays that would be able to evaluate and identify endocrine disrupting chemicals. We would like to introduce the system of testosterone synthesis as a possible biomarker for evaluating environmental chemicals.

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The immature stages (from egg to pupa) of Culex pipiens molestus (Diptera, mosquito) individuals were exposed to 1, 10, 100, and 1000 μgl^-1 of bisphenol A and p-nonylphenol, respectively, with 3 replicates, Hatchability was not affecte significantly at an concentration. Larval mortality increased from 8.5% in the controls to 12 to 22% in the exposed organisms. The emergence rate of the pupae slightly decreased from 0.97in the controls to 0.94 to 0.97 regardless of exposure concentration. The sex ratio of adults (female/male) exposed bisphenol A changed markedly from 1.07 in the controls to 4.70, 3.14 and 0.36 at 100 and 1000 μg1^-1, respectively. Exposure to p-nonylpheriol resulted in an increase in the sex ratio between 1.95 and 2.28. The weight of adult males was not affected, while that of adult females decreased with increasing exposure concentrations of the compounds. This may be partly due to the appearance of small females (body weight, ca. 50% of normal female) that emerged from pupae exposed to high concentrations of the two compounds. Hatchability of each egg raft oviposited emerging females decreased from 96.9% in the controls to 25.0 and 55.6% when exposed to 100 and 1000 μg1^-1 of bisphenol A, respectively. The decrease in hatchability and a delay in emergence may have been due to the decrease in the proportion of males.

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Biomonitoring using duckweed is an efficient method for assessing overall herbicide effects on river ecosystems. Two species of duckweed, Lenna aoukikusa and Spirodela polyrhiza (Lemnaceae), and Ricciocarpus natans (L.) (Bryophyta) were floated individually for 14 d in a flowthrough aquarium carrying pesticide-polluted water from the Sakura River, and growth was measured at 4, 7, and 14 d. Each test was begun weekly or biweekly and was conducted under continuous light from April to August of 1996 and 1997, Growth of the 3 species was greatly suppressed from spring to early summer, when the river water was polluted with several herbicides. Growth of L. aoukikusa, in particular, was almost completely inhibited. This is attributed to several herbicides based on the analysis of river water samples and a Selenastrum (alga) growth test with herbicides detected in the river, Growth of Selenastrum was also suppressed in May in 3-day tests, which were conducted 3 times a week from April to August. However, the Selenastrum recovered by the end of May, although growth of L. aoukikusa continued to be severely suppressed until late June. Biomonitoring using duckweed can continue when river water becomes muddy after heavy rain because it floats on the water surface

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Growth of a freshwater mussel, Anodonta woodiana japonica, reared in an artificial stream receiving river water polluted with agricultural pesticides was investigated. The growth rate of mussels was controlled mainly by water temperature and concentration of phytoplancton however the mussel growth rate from June or July to the beginning of August both in 1996 and 1997 was much smaller than that estimated with a model that uses these factors. In those summer periods, the river water had been polluted with some agricultural pesticides, and the effect of such chemicals in river water may be an important factor on the growth of the mussel. Various methods of setting the mussels were compared to develop as a biomonitoring method using the mussel in situ.

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Using an image analyzer, behavioral changes of the freshwater shrimp, Paraiya compressa improvisa, were investigated within a controlled laboratory setting on the Sakura River, Japan. Increasing shrimp mobility corresponded to sublethal concentrations of pesticides detected in river water during the rice-cultivating season. The chemicals causing high shrimp mobility were removed by filtration with an activated carbon filter. Shrimp mobility in the untreated river water was 3 to 10 times higher than in the filtered river water, The growth rate of shrimps, measured over one month in the summer, was lower for those in the unfiltered river water than in the filtered river water. The results suggest that an image analyzer is a useful tool biological early warning system to monitor chemicals in river water, and behavior analysis of P.compressa improvisa can detect sublethal effects in an actual environment.

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