Technical report: short-term impact of pyraclofos (a new organophosphate compound) on the non-target fauna in tropical environment

--ÿ PROGRAMME DE LUTTE CONTRE UONCHOCERCOSE EN AFRIQUE DE L'OUEST ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA Service de Surveillance de I'Environnement Environmental Monitoring Service Technical report ocPNcu/EMs/go.r Short-term impact of pyraclofos (a new organophosphate compound) on the non-target fauna in tropical environment SHoRT-TERM IMPACT OF PYRACLOFOS (A NEW ORGANOPHOSPHATE coMPouND) ON THE NON.TARGET FAUNA IN TROPICAL ENVIRONMENT Yaméogo L., Tapsoba J.M. and Bihoum M. Onchocerciasis Control Programme B.P. 549, Ouagadougou, Burkina Faso ABSTRACT Among the many larvicides tested against Simulium damnosum s.l. larvae, the vector of human onchocerciasis in West Africa, pyraclofos gave interesting results. Tests were then performed both in laboratory and field conditions to evaluate its toxicity on the non- target aquatic fauna. In experimental short-term gutter tests, the total entomofauna detachment was 29Vo against lSVo for temephos and 58ÿo for chlorphoxim. Centroptilum + Baetls and Pseudopan4ota bertrandi were the most affected organisms. The treatment of a river resulted in a considerable detachment of the same ta,xonomic groups, plus Orthocladiinae. On the other hand, investigations conducted in tanks showed that the 24-hr LC50 for Chrysichthys nigrodigitatus is 150 ug/l and that for Pollifnyrus isidori 170 ng/|, values which are not very different from the operational dose of the larvicide (s 100 ug/l/10 min.). Nevertheless in river, no fish mortality was recorded. It was concluded that pyraclofos at 100 ug/l is less toxic in the short-term than permethrin, carbosulfan and chlorphoxim. Key'words - pyraclofos, entomofauna, antiblackfly, gutter, correspondence analysis. INTRODUCTION Human onchocerciasis (or "river blindness") is a filarial disease transmitted in West Africa by the female of a little humpbacked blackfly, Simulium damnpsum s.1., whose larval instars breed in swift-flowing portions of medium and large rivers. It is a disease which causes skin and then severe ocular lesions followed by blindness and was, for many years, a major public health problem and an obstacle to the socioeconomic development of the fertile valleys in many West African countries. ln 1974, seven of these states, undertook, under the auspices of WHO, UNDP, FAO and the World Bank and with the finanpial support of many donor countries and institutions, to control the disease. 2Because of the absence of an effective drug for mass treatment, it was decided to calry out weekly larviciding against the aquatic stages of the vector. Temephos, an organophosphorus insecticide, in a 20Vo emulsifiable concentrate formulation, was used up to the appearance in 1980 of resistance to this insecticide and then to chlorphoxim (another organophosphorus compound) in certain forest cytotlpes of the vector (Guitlet et al., 1980, Kurtak et al., 1982). These findings led to the large-scale use of Bacillus thuringiensis H-14 (Kurtak, 1986) and to an acceleration of a screening programme in a search for possible alternative lawicides. This acceleration became all the more necessary and was recommended by the Ecological Group (an independent statutory body of the Programme) because of the extension of the Programme area. It is with this in mind that permethrin and carbosulfan were selected among many candidate antiblackfly larvicides (Yaméogo et al., 1983). Recently, pyraclofos has proved to be an effective insecticide against the blackfly. Tests have been carried out to evaluate its toxicity for the non-target aquatic fauna. This paper presents part of the results recorded with regard to this compound. CHARACTERISTICS OF THE PRODUCT §raclofos (ISO draft), with the chemical name of (RS) - (Q-1-(a-chlorophenyl)- pyrazol-4-yl-Q-ethyl S-propyl phosphorothioate), is an organophosphorus compound whose molecular weight is 360.80 (Kono, 1988). It is soluble in water up to 30 ppm at 20oC, and soluble also in alcohol and acetone. Its density is 1.271(28"C). §raclofos can be hydrolysed with a chemical half-life time in water at pH 7 and at temperatures of 25 and 37oC of 700h and 190h respectively. It is biodegraded at a fast rate, especially in eutrophic waters. Hydrolysis would also occur at basic pH level. Bio-accumulation is unlikely to occur (as with other organophosphorus insecticides), mainly because of metabolic degradation. The formulation used in the trials was a 5O7o emulsifiabte concentrate pale yellow in colour. It is an insecticidefacaficide produced by the company Takeda Chemical Industries Ltd. It acts by contact and ingestion. The dose effective against S. damnosum in the Programme area is between 0.05 ppm/10 rnin. and 0.1 ppm/10 min. MATERIAIS AND METHODS The toxicity study was carried out in laboratory and in river using the techniques now well known in the Programme area: acute toxiciÿ in tanks for fish (Yaméogo et al., 1990), gutter tests, sampling of entomofauna drift (Dejoux 1975 and 1981, Troubat, 1981, Yaméogo 1984 and 1988), pre- and post-larviciding qualitative observations. The species used.for the tests are those representative of the study area and which adapt themselves well ro the working conditions. 3During the operational field trial conducted on the White Bandama in Côte d'Ivoire in 1989, different sampling sites were set up and the number of spraying points along the treated section of the river increased frorn the beginning to the end (figure 1). The evolution of the discharge of the river at Niaka is also presented (figure 2). $rraclofos is a product for which only little information wis available on the carry. Moreover, because of the heavy rainfall experienced in the area coneerned in 1990 the breeding sites on the many small tributaries of the lVhite Bandama became active resulting in the presence of flies on the principal course, though it was not colonized by S..damr.rosum larvae. There were considerable fluctuations also in the discharge of the t{/atercourse so that the larviciding tactics had to be modified (location of spraying points in relation to the breeding sites, number of spraying points on the treated reach, etc.). This exceptional situation was at the origin of a particular insecticide pressure on the watercoursê*towards the last weelcs of the operational trial. At present, the carry of pyraclofos is better known (20 to 25 krn at 100 m3/sec). Cases of overdosing related to an overlapping of insecticide waves can therefore henceforth be avoided. RESULTS AND DISCUSSIONS l.Gutter tests on aquatic entomofauna The experiment was carried out on the Sassandra river, in Côte d'Ivoire, with pyraclofos bath 039 at 0.1 mg of active ingredient /l/10 min., in comparison with temephos batch... at 0.1 mg a.i/l/10 min. and chlorphoxim batch... at 0.05 mg a.i./l/10 min. in the preseuce of an untreated gutter. Drift in the control gutter It was very low (SVo detachment) compared to that usually obtained in this tlpe of exoeriment. Amohiosvche senesalensis. a trichooteran soecies. the Simuliids and Chironomini presented a detachment of more than the mean of the total drift in the gutter, but it did not exceed 157o. T\is should be considered as an indication of good experimental conditions. Imoact of temeohos Apart from the Simuliidae which presented a detachment of more than 98Vo and one ephemeropteran ta,xon (Centroptilum + Baetis) which was affected up to 857o, most of the other taxa seemed to be little perturbed with a detachment which was less than 20Vo. The total detachment of the fauna was about 1770, a value which is within the range of values usually obtained with this pesticide at the dosage of 0.1 mg/l/10 min. 4Imp.act of chlorphoxirq Among the non-target organisms, here again, it was the Ephemeroptera (mainly Centroptilurq + Baetis but Pseudopannota bertrandi and Tricosrthus also) which were affected most by this larvicide (almost 85To detachmen$. The effect on the Trichoptera as a whole was average but Amphipsychq senegalensis seenrs to be more susceptible (627o dctachment) than the other species tested. The Chironomidae (Diptera) are also not very susceptible to chlorphoxim even if, as for the other ta:ronomic groups, this product induced the highest detachment. The total percentage of drift due to chlorphoxim uras almost 59Vo, a value which is within the range of the data reported in Yaméogo et al., 1988. Impact of pyraclofos Most of the organisms tested presented low percentages of detachment (tess than 40Vo) except Centroptilum + Baetis and Pseudopannota bertlandi. The susæptibility of Trichoptera is very low. That of Chironomidae is higher but the mean value of detachrnent of this taxonomic group is nearly 25Vo. In the gutter treated with this larvicide the trend of the curve of the percentage of total detachment is very close to that of temephos atd 24 hours after treatment, less than 35Vo of. the fauna had drifted from the gutter. Comparative impact of the three larvicides Since the tests were carried out on the same day and under the same conditions, with a faunal composition @mparable from one gutter to the other, the main factor that could be the cause of the differences recorded in the detachment is the nature and/or dose of the insecticide. This makes it possible to compare the insecticides tested by a direct comparison of the total drift of the organisms in the gutters (Fig.3). Considering the percentage of detachment, the classification of the principal taxa can be made as shown below for the three larvicides tested: femepnos (O.lmg /l/lOminl too ch Ccntr. + 8oeli. Pseud. Centr. +8oeti. Amphi. Tonyt. Cheum. Chiro. Orrho. Chiro. Pseud. Orrho. Amphl. Tony I Cheum. Trico. e-/o O% Lægend Centr. + Baeti. Centroplilum + Baetis Pseud. Pseudopannota bertrandiTrico. Tricorythidae Amphi. Amphypsyche senegalensisCheum. CheumatopsycheChiro. ChironominiTanyt. Tanytar.siniOrtho. Orthocladiinae While at the operational doses Centroptilum + Baetis were the organisms affected most by the organophosphorus compounds, the classification of the susceptibility of the taxa varies from one larvicide to another for the other organisms. On the other hand, a regrouping of the organisms into Ephemeroptera, Trichoptera, Diptera- Chironomidae, Diptera-Simuliidae and other organisms gives the same classification, i.e. from the less to the more susceptible. Trichoptera < Chironomidae < Ephemeroprera < Simuliidae Finally, the diagrams on the classification of the principal t&\a according to their susceptibility reveal two distinct groups of organisms for pyraclofos and temephos: - Centroptilum + Baetis , on the one hand, which are very susceptible and could be affected most in the long term by the weekly spraying of these larvicides; - the Chironomidae, Cheumatop.syche, (Trichoptera), Tricor,vthus (Ephemeroptera) and Pyroctofo§ (tot 039, (O. lrng /l /lO mlnl looy" Amphl. Ortho Chlro. Tonyt Chlorp h or irn (Q.OS mg/ t/ lO minl IOO o/c Cenlr. + Boell. Pseu d. Trico. Cheurn. Tîico 6Amphipsyche, (Trichoptera), on the other hand, which do not appear to be very susceptible to the effects of pyraclofos and temephos and should therefore be able to withstand the impact of the larviciding if other phenomena were not to come into play. On the other hand, for Chlorphoxinr, Trico.rythus with Centroptilum + Baetis and Pseudopannota bertrandi, (Ephemeroptera) constituted the most susceptible taxa- Cheum4topsyche falcifera, C. digitata and the Tanytarsini presented an average susceptibility while Amphipsyche senegalensis (Trichoptera) is more susceptible than this group of organisms but less than the previous one. "JA correspondence analysis (Benzécri 1983 €t 1986) made on data collected from several gutter tests with carbosulfan (a carbamate compound), permethrin (a pyrethroid), temephos, chlorphoxim and pyraclofos (organophosphorus compounds), shows a clear separation on the Fll axis between the most selective larvicides (temephos and pyraclofos) on one side, and permethrin, carbosulfan and chlorphoxim on the other side (fig.a). The inertia percentages of the first trro a:res of the Fl x F2 plane are 377o and 27Vo, i.e., a total of 647o. The Tanlpodiinae seem to be particularly affected by temephos, on the F1 axis, as against the Caenidae and Tricorythidae which are influenced by carbosulfan, chlorphoxim and permethrin. Among the other Chironomidae, Chironomini and Orthocladiinae seem not to be very much affected by these larvicides. It emerges therefore from this experiment that all the organisms do not completely present the same reaction to insecticides belonging to the same chemical family. Furthermore, generally speaking, a marked impact of the larvicides should be expected on the Ephemeroptera in the long ternu However, the monitoring, which has been going on for some fifteen years now in the watercourses treated in the Programme area (Yaméogo et al., 1988), shows a rarefication of the Tricorythidae and certain Baetidae species in the worst cases. Contrary to all expectations, a marked presence of Pseudopannota bertrandi has been observed in certain hydrobiological monitoring stations (OCP Annual Hydrobiolory Report, 1989). 2. Study of the impact of an operational treatment on the insects The results presented in this section are those recorded during the operational trial of pyraclofos batch 082 on the tilhite Bandama during the high-water period; an operational trial being a trial covering hundreds of kilometres of a river section using helicopter and operating as in a real larviciding campaign. Drift sampling with double nets and qualitative observations were the only techniques under which the experiment was conducted. 74§-hf .drifl cyslç at 3-00 metrçp, frop the spraying point (station 2) Before treatment, the trend of the drift intensity curve was of the classic ÿpe; low during the day, the drift increased at night to reach 33 individuals per m3 of filtered water, and then decreased regularly (Fig.S). After treatment, the drift collected for almost 4 hours was comparable to that of the eve at the same time. The drift index increased only a short time before sunset, then fell to merge with the eve's biological-activity drift. This increase which occurred only more than four hours after the application of the product was not due to a delayed effect nor did it correspond to the night drift. It could be due to the larviciding made at 73.4 km upstrearn" ten minuteg before that made at 300 metres from the sampling point. Twice greater than the pre-treatment night drift, the peak occurred two hours earlier and was influenced by the Chironomidae while the Ephemeroptera made up the greater part of the pre-treatment drift (Fig.6). On the whole, the drift remained low at this station, marked by the abundance of early larval stages and the almost complete absence of surface Hemiptera in the collections. 48-hr drift cycle at 5 km from the spraying point (station 3) Just as at the previous station, the pre-treatment drift was of the classic type. It was however more diversified here, indicating different mesological conditions. Since the nearest spraying point upstream was located at 5 km from the sampling area, the drift intensity increase occurred t hr 30 min. after treatment, inJluenced mainly by the Diptera-Orthocladiinae. Of greater magnitude than that recorded at 300 metres from the spraying point, the drift intensity subsequently decreased but another peak occurred in the night with the acrophase being around 22h00 (Fig.7). The Orthocladiinae, Simuliidae, Baetidae (Centroptilum + Baetis), and Hydropsychidae (Aethaloptera) presented drift curves having more or less the same appearance. The Caenidae and Iæptophlebiidae did not seem to have been particularly affected by the treatment. After treatment, the relative composition of the communities underwent an evolution similar to that of the previous station; the Chironomidae became the most represented, followed by the Ephemeroptera, the Trichoptera and the Simuliidae (Fig.8). The drift here was greater than at 300 metres from the spraying point and the second peak recorded around 21h00 could be due to a combination of several factors including the natural night drift, probably intensified by a weakening of the organisms, and the effects of a second pyraclofos wave from the treatment point located some 20 km upstream. 3. Imoact on the fish fauna Acute laboratory toxicity The test concerned mainly Chrlrsichthys nigrodigitatus and Pollimyrus isidori, nvo species quite common in the study area. C. nigrodigitatus (Bagridae) - Iacépède 1803 is known in the Gambia, Senegal, Niger and Volta basins and in most coastal rivers. The ma:<imum standard length is 475 mm but the average length of the individiuals tested was 65 mm. The species feeds mainly on insect larvae (Chironomidae) but also on small mollusca, zooplankton and Hemiptera (Iauzanne in Lévêque et al., 1988). P. isidori (Mormyridae)-Norman 1923 is a small species well known in the Niger, Gambia, Senegal and Volta basins and in coastal rivers. [t feeds on insect larvae and on zooplankton. The average length of the individuals tested was about 47 mm. The medium lethal concentrations calculated according to the probit anaÿsis (Finney, L952) for different exposure times are not very different for these species(Fig.9). However, looking at the slopes of the mortality curves, it appears that the longer the exposure time, the more the least increase in dose results in considerable P. isidori mortalities while C. nigrodigitatus becomes less affected by slight dosage increases. Apart from the 24-hr LC50 which are higher than the highest dosage used in onchocerciasis vector control (100 ug/l/10 min.), the other data are between 50 and 100 ug/1. Compared to other data obtained with permethrin, carbosulfan and cyphenothrin by different authors, particularly Yaméogo et al., 1990, one will note that pyraclofos has the highest 24-hr rc50 (150 ug/l against 40 ug/|, 82 lug/l and 15 ug/l respectively), which means that this product is less toxic than the others. But taking into consideration the operational doses, it appears that the 24-hr LC50 of pyraclofos is closer to its highest operational dose (O.D) than the 24-hr LC50 of permethrin and its O.D. Besides, the 24- hr LC50 of cyphenothrin is equal to its O.D and the difference between the 24-hr LC50 and the O.D of carbosulfan is somewhat comparable to that recorded with pyrablofos. Immediate river toxicity Direct observations made during the larviciding of pyraclofos in river at the dose of 0.1 mg/l/10 min. did not reveal any fish mortality even though the dose at the spraying point was almost ten times the operational one. Collections were made with drift nets both before and after the pyraclofos sprayings. The results do not show an increase in the drift intensity but a slight change in the relative composition of the communities (Fig.11). Schilbe m),stus (Schilbeidae) 9dominated in the night drift but the proportion of Characidae increased in the post- treatment night drift. On the other hand, the day drift, solely composed of Characidae, was not inlluenced by the pyraclofos application. This product does not seem therefore to have a direct impact on fish in river. The post-treatment decrease in the drift intensity and the increase in the proportion of Characidae are the main facts which should be mentioned. Snaclofos is a new compound so the only data available in the literature are those of the producer. From the above results, it can be seen that the product presents at the operational dose, a toxicity on the aquatic entomofauna which is benreen that of temephos and that of chlorphoxim. It acts particularly on Centroptilum + Baetis and Pseudopannota bertrandi which detached up to more than 807o while the other non- target organisms presented a drift above 407o. While in laboratory pyraclofos presents, for fïsh, a relatively high toxicity urhich increases with exposure time, this has not been confirmed by the results of the river tests. No fish mortality was recorded and the slight behavioural change observed for Characidae (particularly fragile fish) was transient. This change did not result in an increase in the drift (in number) of Characidae. It should be recalled that in river, dilution occurs quickly and the fishes could flee and stay as short as possible in the highest corcentrations of the larvicide waves. Short term-toxicity tests are the first stages of the hazard assessement of a candidate antiblacldly larvicide. As the results presented in this paper show that the pyraclofos formulation used at 0.1 mg/l/70 min does not have a particular marked catastrophic impact on the non-target aquatic fauna, a large scale experiment was undertaken to assess its medium and long-term effects on the aquatic environment. The results will be published when completed. Acknowledgements Many persons contributed to the realization of this work. We would like to thank, in particular, Mr J. Wuillot of the University of Lyon, Mr Fanfodé Kondé of the University of Kankan and Mr B. Coulibaly, Mr L Bakoné Mr B. Dolbézanga and Mr S. Bakayoko of OCP who participated in the data collection during the operational trail of pyraclofos. The fish specimens were fished by Mr Simpore who gave us a highly appreciated help in the laboratory too. Finally, we are grateful to Mr T. Mills who undertook the literary revision of the document, and to all those (drivers and technicians) who, in one way or the other also contributed to the carrying out of these tests. 10 REFERENCES Benzécri, J.P. 1983. Analyse de l'inertie intra-classe par l'analyse d'un tableau des correspondances. [æs Cahiers de I'Analyse des données. 8.3.351-358 Benzécri, J.P. et F. Benzécri, 1986. Pratique de l'analpe des donrÉes. Economie, Dunod,533 p. Dejoux, C. 1975. Nouvelle technique pour tester in situ l'impact de pesticides sur la faune aquatique non-cible - Cahier ORSTOM. ser. Ent. Parasitol., 13 (2): 75{0. Dejoux, C. 1980. Effets marginaux de la lutte chimique contre Simulium damnosum. Techniques d'étude. Rapp. ORSTOM, Bouaké, No 35,64 p. Finney, D.J. 1952. Probit Analysis, 2nd ed. Cambridge University Press, C-ambridge, 318 pp. Guillet, P., M. Escaffre, M. Ouédraogo et D. Quillévéré, 1980. 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