Obsolete pesticides are major public health and environmental concern. Ethiopia is one of the largest stockpiles of obsolete pesticides in Africa. The scope of the problem is dramatically high and significant, where more than 3000 tonnes of obsolete pesticides, much of it over 20 years old, is stored in around 900 sites throughout the country. Inventoriesshowed that, the storage condition of obsolete pesticides is very poor, with leaking drums, burst open sacks, and the stores themselves are in a bad state posing great threat to human health and the environment. The main cause of accumulation of obsolete pesticide in Ethiopia is excessive and uncoordinated donations by donor agencies and purchases of pesticides by the Ethiopian Government and inefficient pesticide distribution. Deterioration of pesticide was also due to inadequate storage condition, lack of trained staff in pesticide management, absence of regular stock inspection and national legislation. Therefore, education to the public about the danger of pesticide is important. Intensive training for staff and other people who are involved in pesticide storage, transport, handling and management should be emphasized. Moreover, donors and the Ethiopian government have to arrange a good communication strategy to avoid over supply.

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The present paper reviews the carcinogenicity study of titanium dioxide（TiO₂），widely used in the production of paints paper and plastics, as food additives and colorants, and increasingly, as nanpoparticles in pharmaceutical and cosmetics products, based on data published in openly available scientific literature. Increased incidence of tumors was reported in rats after exposure to respirable, fine or ultrafine TiO₂ by inhalation or intratracheal instillation. No increased incidence of tumors was noted in mice or hamster after exposure to TiO₂ by inhalation or intratracheal instillation, or in rats or mice given TiO2 by intraperitoneal or subcutaneous injection or by feeding. This review indicates that the incidence of tumors was increased in rats after inhalation or intratracheal instillation of TiO₂　at levels associated with particle overload and persistent inflammation.

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Water quality guidelines have been derived to protect aquatic ecosystems in the regulatory framework of many countries. Direct toxicity assessment（DTA）or whole effluent toxicity（WET）testing has been conducted to estimate the toxicity of complex mixture such as industrial effluents using various bioassays. Most countries adopted acute and/or chronic fish toxicity tests in their regulations. For acute toxicity testing, juvenile or adult fish are normally used, whereas the fish embryo toxicity（FET）test is suggested as the alternative to the acute fish tests in Germany. Although Japanese Ministry of the Environment recently started investigation to introduce the WET system for regulatory purpose, bioassays to be employed are not yet decided. In this paper, sensitivities and practical aspects of fish toxicity tests（FET test and OECD Guidelines 203 and 212）were compared for two fish species, zebrafish（Danio rerio）and Japanese medaka（Oryzias latipes）．Results indicate that O. latipes acute toxicity test was the most appropriate method in practical aspects of regulations. The effect of water hardness on Cu toxicity suggested that the water hardness of effluents should be considered to verify toxicity data and to minimize potential toxicity after dilution of effluents.

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Substances such as Al₃₊, Cu₂₊, Cd₂₊, Zn₂₊, ammonia, atrazine, 3,4-dichloroaniline, linear dodecylbenzene sulfonate, pentachlorophenol and phenol were added to a microcosm （mixed flask culture）constituted of bacteria, Cyclidium, Lepadella, Philodina, Aeolosoma, Chlorella and Schizothrix, and the respiration rate and the production rate were determined. Good correlations were found between the observed maximum concentrations of the substances having no effects on the respiration rate and the production rate in microcosms（M_NOAECs）and the mean values of the no-observed-effect concentrations of the substances in experimental and natural ecosystems（NOECs）．An uncertainty factor for predicting the safe environmental concentrations in ecosystems（PNOECs）from the M_NOAECs was estimated to be 200 from the regression line（log [the mean of NOECs] / log [M_NOAEC]）and the log-normal distribution curves of the NOECs of each substance in experimental and natural ecosystems. The calculated PNOECs covered most of the reported NOECs in experimental and natural ecosystems. The microcosm could be used as a tool for screening tests of substances on generic ecosystem-level toxicity.

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We practiced acute toxicity tests of fenobucarb（BPMC, a carbamate insecticide）on neonates（less than 24 h old）of nine cladoceran species. A positive relationship between 24-h LC₅₀ values（range 3.7 to 130.1 μg/L）and neonate body length was recognized, although two species（Moina macrocopa, M. micrura）showed extremely large LC₅₀ values. Effects of BPMC on reproduction（number of offspring）of six of the nine species were also investigated. Several small species were more susceptible to BPMC than larger species in the reproduction tests. EC₅₀s ranged form 2.8（Daphnia ambigua）to 16.3（D. pulex） μg/L with an exceptionally high value 104 μg/L for M. macrocopa. The mean value of 24-h LC₅₀/EC₁₀ was 11.2±12.8 （n=6），the large variation mainly depending on the shape of the dose- response curve for the number of offspring. Inhibition of acetylcholinesterase （AChE）by BPMC in four cladoceran species（one being the most susceptible, one being M. macrocopa）was positively related to species’ BPMC-susceptibility（as 24-h LC₅₀s）．Differences in BPMC susceptibility of cladoceran species may be mainly depending on AChE（its activity and tolerance to BPMC），although contribution through their body size was also suggested.

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A conventional method for evaluating chemical toxicity on algae is the 72 h algal growth inhibition test. However, simpler, faster, and lower-cost methods are required to evaluate the toxicity of a large number of chemicals. One simple approach is to measure algal growth with an optical technique in a small-scale algal culture. Here we propose measuring delayed fluorescence（DF），a kind of prolonged ultra-weak fluorescence. DF showed correlation with the number of algal cells, and the detection sensitivity limit was 1 x 10⁴ cells/mL in our experimental setup. DF also showed unique characteristics when measuring a mixture of living and inactivated algae, and the DF signal showed a correlation with the living cell content. We also compared dose-response curves obtained from DF and cell density measurements for two chemicals （p-chlorophenol and m-chloroaniline） in a 24 h exposure test. DF measurement was more sensitive than the cell density measurement, especially at shorter exposure times of less than 8 h. The results suggest that DF is a suitable choice of detection method that is expected to allow algal growth inhibition tests to be conducted in a shorter time.

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Morphological alterations of the gill lamellae caused by heavy metal exposure are well known. However, the metal profiles in the gill lamellae have poorly understood. In this study, we attempted to determine the precise distribution of copper in the gill lamellae of the Carassius auratus langsdorfii exposed to copper chloride by microbeam scanning particle induced X-ray emission（micro-PIXE）analysis. Essential trace elements, such as iron and zinc in the gill lamellae were also determined and their distribution was compared with that of copper. Exposure of the fishes to copper chloride resulted in a marked alteration in the gill lamellae; the gill filaments on the gill lamellae were clubbing. Micro-PIXE analysis revealed a site-specific distribution of copper corresponding to the alterations. Copper was found to be high in the periphery of the gill lamellae, and low in the blood vessel and the tissues surrounding the blood vessel. The profiles of copper and the essential trace elements were complementary distribution.

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