[Biological safety of the molluscicidal ingredient from Aspergillus fumigatus SL-30 isolated from rhizosphere of Phytolacca acinosa].

OBJECTIVE: To study biological safety of the molluscicidal ingredient (MI, a kind of diketopiperazines) in the exocellular broth of Aspergillus fumigatus SL-30' which was isolated from the rhizosphere of Phytolacca acinosa. METHODS: The MI was prepared in concentrations ranging from 0.01 to 0.60 mg/L, at the same time molluscicidal activity against Oncomelannia hupensis was tested by using immersion method, and the LC50 in the case of immersion time for 24, 48 and 72 h was calculated. Acute toxicity of the MI with concentration ranging from 0.5 to 4.0 mg/L on Brachydanio rerio, Macrobrachium nippoensis and Rana limnochris was performed by standard laboratory procedure, and mortality rate of the tested animals with treated time of 24, 48 and 72 h was recorded. Effect of the MI on Eisenia fetida was tested using natural soil procedure with the dose of 1 and 10 mg/kg, and the poisoning performance and mortality in the 7th day and 14th day were recorded. Inhibition of the MI at 10 mg/kg on respiration of soil microorganisms was determined by sealed alkaline direct absorption method, and the released amount of CO2 (mg/100 g) in the 2nd, 5th, 7th, 10th, 12th and 15th day was determined. RESULTS: Molluscicidal activity of the MI against Oncomelania hupensis was shown with LC50 0.101, 0.062, and 0.022 mg/L in 24, 48 and 72 h, respectively. Mortality rate of Brachydanio rerio, Macrobrachium nippoensis and Rana limnochris all increased with the increase of MI concentration, and the LC50 of each kind of tested animals was recorded as follows: 1.941, 1.755 and 1.219 mg/L for Brachydanio rerio, 3.170, 2.720 and 2.419 mg/L for Macrobrachium nippoensis, 2.109, 1.751 and 1288 mg/L for Rana limnochris in 24, 48 and 72 h, respectively. The LC50 of MI on Eisenia fetida was >10.0 mg/kg. The inhibition rate of MI was less than 50% with a concentration of 10 mg/kg in 15 days. CONCLUSION: The MI shows molluscicidal activity on Oncomelania hupensis with much lower toxicity on Brachydanio rerio, Macrobrachium nippoensis and Rana limnochrisn. The MI is safe to non-target aquatic organisms, and to both Eisenia fetida and soil microorganisms under the effective mollussicidal concentration.

Impact of certain plants and synthetic molluscicides on some fresh water snails and fish.

The LC50 (78, 85 ppm) and LC90 (88, 135 ppm) of Anagalis arvensis and Calendula micrantha respectively against Biomphalaria alexandrina were higher than those of the non-target snails, Physa acuta, Planorbis planorbis, Helisoma duryi and Melanoides tuberculata. In contrast, the LC50 of Niclosamide (0.11 ppm) and Copper sulphate (CuSO4) (0.42 ppm) against B. alexandrina were lower than those of the non-target snails. The mortalities percentage among non-target snails ranged between 0.0 & 20% when sublethal concentrations of CuSO4 against B. alexandrina mixed with those of C. micrantha and between 0.0 & 40% when mixed with A. arvensis. Mortalities ranged between 0.0 & 50% when Niclosamide was mixed with each of A. arvensis and C. micrantha. A. arvensis induced 100% mortality on Oreochromis niloticus after 48 hrs exposure and after 24 hrs for Gambusia affinis. C. micrantha was non-toxic to the fish. The survival rate of O. niloticus and G. affinis after 48 hrs exposure to 0.11 ppm of Niclosamide were 83.3% & 100% respectively. These rates were 91.7% & 93.3% respectively when each of the two fish species was exposed to 0.42 ppm of CuSO4. Mixture of sub-lethal concentrations of A. arvensis against B. alexandrina and those of Niclosamide or CuSO4 at ratios 10:40 & 25:25 induced 66.6% mortalities on O. niloticus and 83.3% at 40:10. These mixtures caused 100% mortalities on G. affinis at all ratios. A. arvensis CuSO4 mixtures at 10:40 induced 83.3% & 40% mortalities on O. niloticus and G. affinis respectively and 100% mortalities on both fish species at ratios 25:25 & 40:10. A mixture of sub-lethal concentrations of C. micrantha against B. alexandrina and of Niclosamide or CuSO4 caused mortalities of O. niloticus between 0.0 & 33.3% and between 5% & 35% of G. affinis. The residue of Cu in O. niloticus were 4.69, 19.06 & 25.37 mg/1kgm fish after 24, 48 & 72 hrs exposure to LC0 of CuSO4 against B. alexandrina respectively.

Inhibition of coral photosynthesis by the antifouling herbicide Irgarol 1051.

International regulation of organotin compounds for use in antifouling paints has led to the development and increased use of replacement compounds, notably the s-triazine herbicide Irgarol 1051. Little is known about the distribution of Irgarol 1051 in tropical waters. Nor has the potential impact of this triazine upon photosynthesis of endosymbiotic microalgae (zooxanthellae) in corals been assessed. In this study Irgarol 1051 was detected in marinas, harbours and coastal waters of the Florida Keys, Bermuda and St. Croix, with concentrations ranging between 3 and 294 ng 1(-1). 14C incubation experiments with isolated zooxanthellae from the common inshore coral Madracis mirabilis showed no incorporation of H14CO3- from the sea water medium after 4-8 h exposure to Irgarol 1051 concentrations as low as 63 ng 1(-1). Reduction in net photosynthesis of intact corals was found at concentrations of l00 ng 1(-1) with little or no photosynthesis at concentrations exceeding 1000 ng 1(-1) after 2-8 h exposure at all irradiances. The data suggest Irgarol 1051 to be both prevalent in tropical marine ecosystems and a potent inhibitor of coral photosynthesis at environmentally relevant concentrations.

Re-colonisation and recovery of populations of dogwhelks Nucella lapillus (L.) on shores formerly subject to severe TBT contamination.

Dogwhelks Nucella lapillus became locally extinct on some shores adjacent to areas of high shipping/boating activity during the period of high tributyltin (TBT) contamination in the 1980s and early 1990s. However, the species has now re-colonised sites at which extinction occurred on the Isle of Cumbrae, the northeast coast of England, the Shetland Isles and southwest England. There have also been substantial declines in the severity of imposex on adjacent shores where the species has persisted during this period. Re-colonisation and recovery can be attributed to two measures: regulations prohibiting the use of TBT-based paints on vessels < 25 m in length and the development of slow-releasing, self-polishing copolymer paints. Nevertheless, the International Maritime Organisation has now imposed a total ban on the use of TBT-based paints as antifoulants. This is almost certain to result in the use of paints containing alternative biocides and there is widespread concern that there is relatively little information on which to assess their likely environmental impacts. They could cause substantial environmental damage.

Comparative environmental assessment of biocides used in antifouling paints.

In response to increasing scientific evidence on the toxicity and persistence of organotin residues from antifouling paints in the aquatic environment, the use of triorganotin antifouling products was banned on boats of less than 25 m length in many countries during 1987. Alternatives to tributyltin (TBT) paint are mainly copper based coatings containing organic booster biocides to improve the efficacy of the formulation, and have been utilised on small boats for the last 10 years. With policies encouraging a total ban on TBT, it is expected that these biocides will be used to a greater extent in the future. Limited data and information are available on the environmental occurrence, fate, toxicity, and persistence of these biocides, and thus any decisions on policies regulating antifoulants cannot be fully informed. In this study, a multicriteria comparison of alternative biocides, based on a general assessment of available information in the literature, provided support for the use of the precautionary principle with respect to policies on antifouling products. This assessment was validated by a more detailed comparison of four selected biocides and TBT. Results indicate that TCMS pyridine and TCMTB demonstrate environmental characteristics similar to TBT and thus detail risk assessments are needed before their use is permitted. The widespread use of the other biocides should be allowed only after research to fill the gaps in knowledge with respect to their toxicity and persistence in aquatic environments.

Effect of niclosamide on the marketable fish Liza ramada (Risso, 1826) concerning accumulation in muscles and activities of three metabolic liver enzymes.

The accumulation in muscles and the effect of different concentrations of niclosamide (Bayluscide) on the metabolic enzymes; succinate dehydrogenase (SDH), pyruvate dehydrogenase (PDH) and lactate dehydrogenase (LDH) in the liver of the Thin-lip grey mullet after 1, 2 & 3 weeks were studied. The molluscicide residues were detected in the muscles. The residues increased with the increase of concentrations of niclosamide as well as the time of exposure. On the other hand, LDH showed significant increase. But, SDH and PDH showed significant decrease. No doubt, this disturbance in the three liver enzymes cause disturbance in the process of metabolism. The important point is what about man who consumes a fish with niclosamide accumulated in its muscles.

Mammal toxicity assessment of the plant molluscicide, Apodytes dimidiata (Icacinaceae), in South Africa.

Apodytes dimidiata has recently come to the fore as a potential plant molluscicide for schistosomiasis control in rural communities in South Africa. Prior to field applications of its leaves and extract to waterbodies, selected acute and sub-acute mammal toxicity tests were conducted in accordance with the Organisation of Economic Cooperation and Development (OECD) Guidelines to identify any potential hazards that might arise form the plant's use. Acute and sub-acute mammal toxicity test results classified A. dimidiata as non-toxic and non-irritating. Based on this toxicity evaluation, the dried leaf material and aqueous extracts of this plant are considered safe for use in preliminary field trials.

Trials on focal molluscicide application in larger irrigation canals and lakes in Mali.

Schistosomiasis transmission in some irrigation schemes in Mali, appears to be very focal, and mainly occurs in human water contact sites close to villages. On this background, a strategy of focal snail control based on application of molluscicide to such sites only, was to be implemented in these areas. However, transmission often occurs in larger canals and lakes, and in these habitats focal snail control is obviously very difficult. This paper deals with experiments carried out to evaluate the effectiveness of focal application of 70% Bayluscide wettable powder in such habitats. Bayluscide was applied in two different ways depending on snail distribution within the sites. When snails were found in marginal vegetation, 2-3 ppm was applied along the shore (to various distances from the shore) from 10-40 m upstream from the water contact sites to 10 m downstream. In case snails were found in low submerged vegetation, which was very common in these habitats, the chemical was applied at 2-4 g (a.i.)/m2 directly between the plants. The results indicate that a satisfactory snail-kill can be achieved in the target area by this method of Bayluscide application. However, the method requires a thorough surveillance for snails and due supervision of the application. The time spacing of applications should probably be 4-6 weeks, but special situations may necessitate more frequent applications.

Phytotoxicity tests with the molluscicide N-tritylmorpholine.

N-Tritylmorpholine (Frescon, WL 8008) has been applied as an emulsifiable concentrate (FX 28) to cotton and rice in glasshouse experiments without any adverse effects. The compound was applied in the irrigation water at 5 and 10 times the rates used for snail control. The experiment on cotton was terminated after 60 days, when the plants became pot-bound. The treatments did not affect the leaf area or the fresh weight of plants. The rice (Oryza sativa ssp. japonica) was harvested and no differences in growth, time of ear emergence or total plant weight were noted.A further experiment using the same formulation of N-tritylmorpholine in an overhead spray on young cotton and rice, at rates up to 48.5 kg/ha of FX 28, resulted in no adverse effects.