Shigehisa Hatakeyama

Effects of simetryne on growth of various freshwater algal taxa.

The sensitivity of 56 algal strains, representing 7 taxonomic groups to the triazine herbicide, simetryne, was examined using EC50 values for growth. There was a wide range of values from 6.5 to 1500 microg litre(-1). The Volvocales (Chlorophyceae, Chlorophyta) and Cyanophyceae (Cyanophyta) as a whole were the most sensitive, whereas the Desmidiales (Charophyceae, Chlorophyta) and Bacillariophyceae (Chromophyta) were the most tolerant, although sensitivity differed among strains of a single species. Sensitive and tolerant species were both isolated from samples collected at the same site. The results suggest that changes in species composition and relative abundance will occur when herbicides are applied in natural habitats.

Herbicide susceptibility in two green algae, Chlorella vulgaris and Selenastrum capricornutum

Abstract Responses of four strains belonging to two green algae, Chlorella vulgaris and Selenastrum capricornutum to three herbicides, simetryn, pretilachlor and thiobencarb, were compared, using single species toxicity tests for population growth. There was obvious difference in the susceptibility beween the two species. The two strains of C. vulgaris were more tolerant than the two strains of S. capricornutum to all the three herbicides. The difference in the susceptibility between the two species might be explained in part by the characteristics such as a thick cell wall and higher activities of several enzymes in C. vulgaris.

A freshwater shrimp (Paratya compressa improvisa) as a sensitive test organism to pesticides

The susceptibility of 2-week-old individuals of the freshwater shrimp, Paratya compressa improvisa, to five kinds of insecticide and five kinds of herbicide was examined in comparison with that of two species of Cladocera, Daphnia magna and Moina macrocopa. The shrimp was especially sensitive to two organophosphorus insecticides. The 48-h LC50 values for fenitrothion and fenthion to the shrimp were 1.15 and 1.04 microg litre(-1) (mean value, n=2), in contrast with 37.8 and 35.3 microg litre(-1) in the case of M. macrocopa, and more than 50 microg litre(-1) with D. magna. The shrimp also showed the higher susceptibility to other insecticides, diazinon, carbaryl (NAC) and BPMC, apart from D. magna to diazinon and NAC. The shrimp also showed higher susceptibility to herbicides. The 48-h LC50 values of CNP, benthiocarb, oxadiazon, butachlor, and symetryne to the shrimp were two to eight times lower than those of two species of Cladocera, except for the LC50 value of oxadiazon to M. macrocopa, which was very slightly higher. However, the shrimp showed a somewhat lower susceptibility to heavy metals than the two species of Cladocera, especially to copper, and to cadmium and zinc in comparison with D. magna. A bioassay using the shrimp with river water, collected from the river adjacent to the paddy field, showed clearly the high mortality of the shrimp following the aerial spraying with pesticides.

Effect of copper and zinc on the growth and emergence of Epeorus latifolium (Ephemeroptera) in an indoor model stream

Effects of Cu and Zn through food as well as through the water on the growth and emergence of the young larvae of Epeorus latifolium (Ephemeroptera), were investigated using an indoor model stream. The critical lowest concentrations of Cu which have significant effects on the growth of the larvae were between 10 and 15 µg l-1 Cu. Growth and emergence of the larvae fed on the algae (diatoms) which accumulated more than 1000 µg Cu g-1 (dry wt.) were significantly impaired. Growth of the mayfly larvae exposed to 100 or 300 µg l-1 Zn ceased after the second week, and all died before emergence. At 30 µg l-1 Zn, the growth rate decreased gradually and many larvae died before emergence. The molt interval also nearly doubled that of the control at these concentrations. Growth and emergence of the mayfly fed the algae which accumulated more than 2000 µg g-1 of Zn were significantly affected.

Tolerance to cadmium and cadmium-binding proteins induced in the midge larva, Chironomus yoshimatsui (diptera, chironomidae)

Abstract 1. The midge larva ( Chironomus yoshimatsui ) was exposed to cadmium (10 μg Cd/ml) for 2 days. 2. A large portion of cadmium taken up rapidly into the insects was bound to the high molecular weight proteins and was rapidly discharged in control water. 3. Low molecular weight cadmium-binding protein was slowly induced in the larva by cadmium exposure. This protein was a mixture of four isoproteins and showed the characteristic properties of metallothionein. 4. The high tolerance of the midge larva to acute cadmium exposure was not explainable by induction of the cadmium-binding proteins.

Assessment of herbicide effects on algal production in the Kokai River (Japan) using a model stream and Selenastrum bioassay

The effects of herbicides on algal production in the Kokai River were assessed using a Selenastrum growth inhibition test and by an investigation of the periphyton formed in a channel carrying river water. Herbicides in the water were analysed at the same intervals as the algal growth test (three times per week) from April to August 1992. Growth of Selenastrum in the river water samples was inhibited severely in mid-May, mostly by the joint effects of butachlor and pretilachlor and from early to late June mostly by simetryn alone. The influence of six other kinds of herbicide was low or not detectable. Selenastrum growth ratios (SGR) in the river water samples were correlated with fluctuations in SG-IP (Selenastrum growth inhibition potential), the sum of the growth inhibition ratios by the respective herbicides at the concentrations detected in the river. However, the expected growth inhibition (SG-IP) was usually larger than the observed value (SGR); the reasons for this are discussed.The rate of accumulation of periphyton, which formed on a substrate in the channel, decreased from early May and stayed at relatively low levels until early June. The low accumulation rate from mid-June to mid-July, when growth of Selenastrum had almost recovered, can be attributed to grazing by invertebrates. These results suggested that algal production in the Kokai River is affected by the single or joint action of herbicides, at least in the period from early May to early June.

Monitoring of the overall pesticide toxicity of river water to aquatic organisms using a freshwater shrimp, Paratya compressa improvisa

Abstract River water samples were bioassayed from July 1988 to March 1989 using the freshwater shrimp, Paratya compressa improvisa , to establish the variation in the overall toxicity of the rivers to aquatic organisms. Water was collected from four sampling stations in the three small rivers surrounded by paddy fields. The 4-day mortality of the shrimp increased to 100% for several days after aerial spraying of insecticides and fungicides, which was conducted between late July and early August. However mortality gradually decreased to a few or zero percent by the end of August and showed similar low values until the end of the survey in March 1989. The cause of the high mortality of the shrimp is attributed largely to the pesticides, such as fenitrothion, fenthion, and/or BPMC (organophosphorus insecticide), although the contribution of herbicides and fungicides is unclear at the present time. While, high mortality of the shrimp suggested an existence of another toxic pesticides, which were overlooked in routine analysis.

Chronic effects of Cu on reproduction of Polypedilum nubifer (chironomidae) through water and food

The effects of Cu on the reproduction of Polypedilum nubifer (Chironomid) through water and food were examined in a flowthrough aquarium by Cu exposure from the egg stage. The emergence success decreased to 74, 38, 16, and 2% of the control at 10, 20, 30, and 40 micrograms Cu/liter, respectively. However, the oviposition success (No. of egg clusters/female) remained at 64% of the control value even at 30 micrograms Cu/liter. From these results and the acute toxicity test, it was suggested that a decrease in emergence success was caused mainly by mortality in the early instar stage, when Cu sensitivity is high. There were no significant effects of Cu on the emergence success, oviposition success, and hatchability of the oviposited eggs in the midge which had been given food contaminated with about 330 micrograms Cu/g (dry weight). However, emergence success and hatchability of the oviposited eggs decreased to 30 and 40% of the control in the midge which had been fed food accumulating 1770 micrograms Cu/g, although the oviposition success was not impaired compared to the control. Emergence did not occur from the aquaria fed food accumulating 5200 micrograms Cu/g.

Changes in the benthic fauna and flora after application of temephos to a stream on Mt. Tsukuba

A dose of 2 ppm of temephos in emulsifiable formulation was applied to a mountain stream to observe its effects on the zoobenthos and the subsequent changes in benthic algae. Most zoobenthos in the treated region drifted but there were slight differences among taxa. Ephemeroptera and Plecoptera disappeared but some Trichoptera and Diptera survived. Chironomids recolonized earlier than other invertebrates and reached a higher density level than before the treatment. A bloom of benthic algae occurred following the destruction of fauna. The increase in the standing crop of algae was accompanied by an increase in the number of species. Among these, Achnanthes lanceolata, Meridion circulare and Tetraspora gelatinosa were predominant. The end of the bloom began with the recovery of the zoobenthos population.

Accumulation and effects of cadmium on guppy (Poecilia reticulata) fed cadmium-dosed cladocera (Moina macrocopa)

The study examines the rate of cadmium uptake and body burdens which cause adverse effects on the survival and growth of guppies when they are exposed to Cd dosed in zooplankton (Moina macrocopa) and Cd dissolved in water. Eight guppies fed Moina dosed at 20 ..mu..g Cd/L water died before 10 days. Growth of the remainder of the guppies exposed at this rate was impaired initially but was returned to control level around the 10th day of the study. (JMT)