Controlled Release Polymeric Formulations - ACS Publications

17 Development of Field Evaluation of Controlled Release Molluscicides: A Progress Report KATHERINE Ε. WALKER

Downloaded by TUFTS UNIV on September 29, 2014 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0033.ch017

Engineering and Science Division, Community and Technical College, University of Akron, Akron, Ohio 44325

Introduction One vital aspect of public health programs in most tropical nations l i e s i n the control of parasitic diseases. The major snail-borne disease, Schistosomiasis or Bilharzia, may have as many as 300 million human victims with several million deaths annually attributed directly or indirectly to it. Although death is the ultimate tragedy, all those a f f l i c t e d suffer a loss i n physical prowess and often in mental a b i l i t y . Since the victim is usually an agricultural worker the disease manifests i t s e l f as a loss in agricultural output and the national economy is depress ed accordingly. A free swimming larva, the cercaria, develops from asexual reproduction i n the snail. Released into fresh water it must find a human and penetrate the dermis. The cercaria can not obtain sustenance nor reproduce so i t s "infective life" seldom exceeds twelve hours. The successful penetrant travels via the circulatory system to the mesentaries around the l i v e r , spleen and bladder. Here development inot the adult worm takes place. Paired male and female worms produce massive numbers of eggs continuously. The ova must reach the external environment, and this i s achieved via human excretion. An ovum i n water hatches into a free swimming, non-reproduc t i v e , non-feeding larval form, the miracidium. I f the miracidium finds a snail of an appropriate species i t penetrates and under goes changes that lead to the asexual reproduction of cercaria, thus completing the cycle. An infected s n a i l may release several thousand cercariae per day, but this usually represents only a few per cubic foot of water. Of the thousands of eggs produced by the worms i n the human body only a certain percentage reach the appropriate ex ternal environment, with further a t t r i t i o n during hatching and snail location. However, a great number of the eggs never leave the human body. They remain entrapped i n capillaries and various 215

In Controlled Release Polymeric Formulations; Paul, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

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organs. Tissue damage and a general debility can only lead to secondary infections and overall lowered resistance.


Control Methodology The conventional approach to Schistosomiasis control l i e s i n the use of chemical agents, molluscicides, to interrupt the parasite transmission cycle by destruction of the s n a i l intermediate host. Medical therapy i s useless i f contact with infested water is not prevented and immunization i s not yet possible. The major molluscicides used are copper sulfate, niclosamide, trifenmorph and several pentachlorophenols. These are applied to snail habitats as wettable powders, granules, solutions or emulsions. Unfortunately i t i s l i t e r a l l y impossible to locate and treat a l l snail habitats in a given locale, and even in treated waters a small, but relevant, number of target snails w i l l successfully undertake avoidance behavior. Repopulation i s rapid from even quite isolated f o c i i and periodic retreatment becomes essential. Economic resources are, in general, grossly inadequate in the endemic nations to permit undertaking of the massive mollusciciding program required and the necessary reapplication of the chemi c a l every few months. It i s generally acknowledged that the worldwide struggle against Schistosomiasis using conventional approaches is f a i l i n g (1). In concept the use of controlled release molluscicides would allow the extension of the between treatment interval to years, provide more effective control at less cost and substantially decrease the amount of control agent utilized thus lessening impact on the non-target biota. Controlled release also makes attack of the miracidium, cercaria, and ova practical. Development of Controlled Release Materials The precursor of controlled release molluscicides is the organotin containing antifouling elastomeric formulations developed in I96U (2,3). The resulting 6$ active chloroprene sheet rubber material has been commercialized and applied to ship hulls, buoys and other marine objects (i*,5). The i n i t i a l f i e l d applications on bouys in 1966 remain biologically effective to date (6). That is , a chemical agent, bis(tri-n-butyltin) oxide "TBTO, h a s b e e n continuously r e l e a s e d in l e v e l s commensurate with t h e prevention of fouling for over 9 yearsi Inthis and other controlled release applications a cost benefit of 7 to 1 or greater i s realized and a reduction of 10 to 1, or greater, i n terme of environmental contamination(7,8). The very long term sustained release materials are based upon solution equilibrium properties common to elastomeric matrices. An agent highly soluble in the elastomer i s placed in solution i n the given material—natural rubber, styrene-butadiene copolymers,



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cis polybutadiene, etc., upon water immersion surface agent molecules undergo gradual dissolution into the rubber/water interface thus disturbing solution equilibrium. Concomitantly internal solute molecules migrate towards the depleting surface due to solution pressure—and a gradual surface release cycle i s established. The s o l u b i l i t y of the agent in water ought to be quite small. System kinetics may be f i r s t or second order depending upon whether diffusion or dissolution i s rate controlling (1)· Controlled release antifouling materials were found toxic to various s n a i l species (3*9)· T r i a l k y l t i n s , such as TBTO and t r i butyltin fluoride "TBTF*, and niclosamide were successfully i n corporated i n various elastomers and through proper compounding techniques and vulcanization conditions caused to release at a slow continous rate when immersed i n water. Laboratory studies performed at the University of Akron demonstrated that various controlled release antifouling elastomers would destroy snails at ultralow toxicant release concentrations (i.e. 0.01 ppm or l e s s ) . In Tanzania such materials were examined under semi f i e l d conditions—i.e. f i e l d water continuously flowing through a laboratory bioassay tank and i n small ponds confirming that mortality did ensue (10). Laboratory tests in Puerto Rico likewise provided positive results (11)· I Brazil antifouling rubber sheet strips placed i n irrigation reservoirs and ponds provided complete snail mortality—within k$ to 60 exposure days (12)· Tests i n London (Tropical Pesticide Research Headquarters) demonstrated that the biological efficacy of a given rubber pellet was i n excess of two years (13). The formulations involved were laboratory specimens and not optimized products. n

Controlled Release Molluscicides ("CRM") In 1972 the Creative Biology Laboratory (Barberton, Ohio) working under the auspices of the M&T Chemical Company (Rahway, New Jersey) undertook the optimization of a TBTO/natural rubber formulation. This effort culminated i n the 6f active material now available as BioMet-SRM. In other effort sponsored by the World Health Organization a TBTF/natural rubber CRM was developed to further enlarge the controlled release arsenal (1^)· These substances function through a diffusion-dissolution loss mechanism dependent upon agent s o l u b i l i t y within the elastomer (15)· In a p a r a l l e l program a CRM composed of copper sulfate i n an ethylenepropylene-diene rubber base was developed and i s now commercialized as INCRACIDE E-51 (international Copper Research Organization, New York, New York) (l§). This l a t t e r material functions through a leach type mechanism using an ammonium sulfate coleachant to maintain appropriate rubber/water i n t e r f a c i a l pH. Formulations present no d i f f i c u l t y i n mixing, extruding, vulcanizing and p e l l e t i z i n g . Natural rubber, ethylene-propylene terpolymers, polychloroprenes, and polyacrylonitriles w i l l retain considerable quantities of the organotins i n solution and bind up to 0


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70$ by weight of copper sulfate. Field Studies Biomet* SRM was applied at rubber dosages of 50 ppm ( 3 ppn active) to stationary water bodies such as ponds and marshes; and several running water channels in Brazil. Seventeen small test sites were thus established (17)· Sanil populations were reduced to zero in the static systems within a few weeks and no repopulation was observed over the course of the 1^ month program. Macroscopic ovservation of vascular water plants showed no discernable damage althouh some reduction in algae was apparent. Snail destruction was insufficient in the flowing water tests. Control has also been demonstrated in lake and reservoir tests in Rhodesia (18). BioMet SRM rubber strips and pellets were applied to irrigation reservoirs of an acre or more in sur face area, irrigation channels, aid along lakeside contact points. CBL-9B pellets were also applied to lake environments. Organotin containing antifouling paints were coated on the concrete walls and other structures of promary irrigation canals and weirs. A l l tests have given positive results to date—both in static and cynamic running water systems. Treatment dosages were but a few parts per million. Snail mortality was not observed until sev eral months after application, and then populations dropped very rapidly—approaching zero. Focal control, i.e. treating only the human-snail interaction points or areas of large snail populations rather than area control, appears on the basis of the Rhodesian experience to be the proper approach to intervention. Organotin paints are adequate for perhaps one year and the controlled release organotin elastomers for 2 or more years—based on Rhodesian results. Analysis of pellets returned after ih months of exposure in Brazil showed a 15$ to 20$ loss of the ac tive agent—thus allowing a 2.5 year half-life prediction. Comprehensive analysis of non-target test site biota in Rhodesia disclosed l i t t l e environmental impact on vascular plants, oligochaetes, water insects, algae, daphnia and other life forms. No fish intoxication was observed (19). Direct observation, time lapse photography, and analysis of treated water, bottom soil, subsoil etc. strongly indicates that the organotin content in treated water is very minute—in the low parts-per-billion at best—and that i t concentrates in the bottom soil where browsing snails ingest i t (19). This could be ex pected from the extreme hydrophobicity of the organotine. Tests conducted by the author showed that where snail contact with the bottom soil was permitted a LT99 of 8 days could be expected at


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10 ppm rubber (0.6 ppm T3T0 or 3ppm ΤΒΤΓ active) dosages while

snails isolated from bottom soil contact under similar regimens showed an LT99 of nearly 30 days. BioMet™ SRM tests conducted in a flowing water stream in


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St, Lucia, B.W.I., exhibited 100$ snail mortality (20). Static water evaluation in small natural ponds in the Sudan and Iran with BioMet* SRM pellets likewise demonstrated wxcellent snail control and no gross ecological disturbance (21,22). CBL-9B pellets, supplied by the Creative Biology laboratory, have been found effective against the amphibious snail vectors of the Asiatic form of Schistosomiasis (23). In a l l instances one application provided significantly longer control than would be realized with conventional treatments and drastically less environmental impact. Efficacious dosage rates have been in the practical range of 50 ppm pellet (15 or less ppm active) at a l l sites. Since complete release of the active agent will require no less than 2.5 years and such release is continuous through decreasing with time—an average site con centration would be about 0.016 ppm. The actual water concen tration likely does not exceed 0.002 ppa—the rest being absorbed by soil, plants, etc. Being relatively l i t t l e organotin dissol ved in the water, there is l i t t l e available to fish and other beneficial elements of the biota (35 )· MLcroenvironmental lab oratory tests affirm control without gross effects on fish or aquatic vascular plant l i f e , at least with ΤΒΤ0, TBTF and copper releasing formulations (15,2U). Although INCRACIDE E-51 CRM has not been as thoroughly tested as other materials, preliminary results from St. Lucia(20), Rhodesia (25), and the Sudan (26) indicate feasibility. Past and present University of Akron CRM evaluations indicate that release levels of 0.007 ppm/day or less of the trialjsyltins and about 0.03 ppm/day of copper ion are adequate to control host snail populations under varying water quality conditions. pH, mineral content and other environmental factors influence rates of toxicant release from the elastomeric matrix, snail uptake and detoxification mechanisms. CRM dosages are presently being es tablished based upon water quality parameters (27). It is believed that controlled release molluscicides are proving to be an economical and feasible method of intervening in the parasite transmission cycle. The recent decision by the Rbodesian public health authorities to utilize BioMet^ SRM in an area wide control program lends support to the merit of this new approach in snail control. Literature Cited 1. Cardarelli, N.F. (1976) Controlled Release Pesticide Formula tions, CRC Press, Cleveland, Ohio. 2. Cardarelli, N.F. and Caprette, S.J. (1969) Antifouling Cov erings. U.S. Patent 3426473. 3. Cardarelli, N.F. and Neff, H.F. (1972) Biocidal Elasomeric


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Compositions.

U.S. Patent 3639583·

Bollinger, E.H. (1974) Controlled Release Antifouling Rub ber Coating. Rept. 19. Proc. Controlled Release Pesticide Symp. Univ. Of Akron, Akron, Ohio.


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Janes, G.A. (1975) Polymeric Formulations for the Control of Fouling on Pleasure Craft. Proc. Controlled Release Pesticide Symp. Wright State University, Dayton, Ohio. 6. Senderling, R.A. (1967) Rubber World. 157 (2), Nov. 7. Cardarelli, N.F. (1975) Controlled Release Pesticides: The State of the Art. Plenary Lecture. Proc. Controlled Re lease Pesticide Symp. Wright State d i v e r s i t y , Dayton, Ohio. 8. Cardarelli, N.F. Address i n 1975 to the Federal Working Group on Pest Management. NAL, B e l t s v i l l e , MD. (To be pub lished). 9. Cardarelli, N.F. (1968) Method for Dispersing Toxicants to Kill Disease Spreading Water-Spawned Larva, Trematodes, Molluscs and Similar Organisms; and the Products Used i n Such Methods. U.S. Patent 3417181. 10. Fenwick, A. (1969) Wld. Hlth. Org. Inform. Rep. Ser. AFR/ BILHARZ/14. 11.Ritchie, L.S. and Malek, E.A. (1969) Wld. Hlth. Org. Inform. Rep. Ser. PD/MOL/69.1. 12. Paulini, E. and Souza, C.P. da. (1969) Wld. Hlth. Org. Inform. Rep. Ser. PD/MOL/69.9. 13. Hopf, H.S. and Goll, P.H. (1970) Wld. Hlth. Org. Inform. Rep. Ser. PD/MOL/70.14. 14. Quinn, S.A. and Walker, K.E. (1972) Ann. Prog. Rept. to Wld. Hlth. Org. Proj. B2/181/62. 15. Cardarelli, N.F. i n Molluscicides i n Schistosomiasis Control. Ed. T.C. Cheng. Academic Press. 1974. 16. Walker, K.E. and Cardarelli, N.F. (1973) Ann. Rept. to International Copper Research Association. INCRA Proj. 203. 17. Castleton, C. (1974) Brazilian Field Trials of ΜT-1Ε, An Organotin Slow-Release Formulation. Proc. Controlled Re lease Pesticide Symp. Report 22. University of Akron, Akron Ohio. 18. Shiff, C.J. in Molluscicides i n Schistosomiasis Control. Ed. T.C. Cheng. Academic Press. 1974. 19. Shiff, C.J. et. al. (1975) Further Trials with ΤΒΤO and Other Slow Release Molluscicides i n Rhodesia. Proc. Con t r o l l e d Release Pesticide Symp. Wright State University, Dayton, Ohio. 20. Upatham, E.S. (1975) Field Studies of Slow-Release TBTO Pellets (BioMet SRM) Against St. Lucian Biomphalaria glabrata. Proc. Controlled Release Pesticide Symp. Wright State University, Dayton, Ohio. 21. Amin, M. (1975) F i e l d Evaluation of the Molluscicidal Po tency of TBTO i n the Sudan. Prod. Controlled Release Pest icide Symp. Wright State University, Dayton, Ohio. 22. Mansoori, A. (1975) Brief Summary of the Study on ΜT-1Ε Slow Release Molluscicide. Controlled Release Molluscicide Newsletter. University of Akron, Akron, Ohio. 23. Santos, A. (1975) Summary of Results of Laboratory Screen ing of Compound 443A Against O. quadrasi. Controlled Re― tm


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24. 25. 26.


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lease Molluscicide Newsletter, University of Akron, Akron, Ohio, Cardarelli, N.F. (1975) Microenvironmental Evaluation of Slow Release Molluscicides. Proc. Controlled Release Pesticide Symp. Rept. 29. University of Akron, Akron, Ohio. Shiff, C.J. and Yiannakis, C. (1975) Controlled Release Molluscide Studies. Controlled Release Molluscicide Newsl e t t e r , University of Akron, Akron, Ohio. Amin. M. (1975) Evaluation of INCRACIDE E-51 Against Biomphalaria p f e i f f e r i and Bulinus truncatus. Controlled Release Molluscicide Newsletter. University of Akron, Akron, Ohio. Walker, K.E. and Cardarelli, N.F. (1975) Quart. Rept. 1 to U.S. Natl. Inst. Hlth. Grant A I 1 1 8 6 1 - 0 1 A 1 .


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