Effect ofOrganotins on FecalPollution Indicator Organisms

andenvironmental watersamples wereexamined forthepossibility thatpollution involving organotin compounds coulddecrease thevalues forindicator organisms whenstandard methods wereapplied totheanalysis ofwatersamples. (CH3)2SnCl2 and(CH3)3SnCl decreased viable counts atabout10to100mg ofSnliter-' (8.4 x 10-5to8.4x 10-4 molofSnliter-'), and tributyltin chloride was effective atabout0.1to1.0mg ofSnliter-' (8.4 x 10-7 to8.4x 10-6molofSnliter-'. Theseconcentrations, particularly forthemethyltin compounds, aregreater thantheconcentrations reported todateforthese compounds inaquatic ecosystems. Thus,organotin compounds alone wouldnotbelikely to causereductions incounts ofindicator organisms measuredbystandard methods. However, itissuggested that, whencombined withother environmental stressors or uponlong exposure,organotins suchasbutyltins may contribute totheinjury ofindicator organisms. Fornearly 100years, indicator bacteria havebeenused successfully tomonitor thebacteriological quality ofwater. Inrecent years, however, ithasbeenrealized that counts of indicator bacteria canbeinfluenced markedly bystressors whichcaninjure orkill indicator organisms andthusgive lowfalse estimates oftheir numbers. Injured organisms-those whichhavebeensubjected to sublethal stresses sothat they will notgrowunder conditions whichsupport thegrowthofuntreated cells-occur inalmostallaquatic environments. Injured coliforms maycomprise 90%ormoreofcertain populations (10). Die-off of Escherichia coli isparticularly evident inseawater inwhich, after aninitial lag, upto90%mortality maybeobserved in3 to5days(35,38).Factors whichmaybeinvolved inthe injury ordeathofindicator organisms include temperature (5,11,12,38),freezing (36), light (12-14), salinity (15), chlorine (8,34),predation (39), competition fromother heterotrophic bacteria (29), toxic organic compounds (4), andheavy metals (1,10,22,24,27,31). Inaddition, sampling andhandling procedures before enumeration canaffect the viability ofinjured bacteria. Amongheavymetals, tinandorganotin compounds can inhibit orkill aquatic microorganisms (18,19,21), including E.coli (16,25,26,41,42).Tincompounds arepresent in fresh, estuarine, andmarine waters (7,19,23,32,33,40), andtheuseoftincompounds isincreasing (43). Moreover, tins canbemethylated intheaquatic environment (9,17,20, 23), whichcanincrease their toxicity after theyenter abody ofwater. Itispossible that organotin compounds inaquatic systems canaffect theresults ofstandard microbiological assays for waterquality. Therefore, weexamined theeffect ofseveral organotin compounds ontheenumeration offecal coliforms andfecal streptococci byusingstandard plating media. Methyltin compounds wereselected because theycanbe formed inaquatic systems, andatributyltin compound was chosenbecause tributyltins arecomponents ofsome antifouling paints usedonboathulls andcanbefoundin