Invertebrates collected from the water distribution system of Worcester, Mass., were found to harbor a variety of bacteria—some of which may be pathogenic to humans—and to protect them from inactivation by chlorine and monochloramine. Currently, the best approach to invertebrate control is elimination of these organisms before they enter the distribution system or physical or chemical modification of their potential habitats within the system.

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Eleven organochlorine and twelve organophosphorus pesticides and one antibiotic were selected from laboratory screening tests for field evaluation in baits for control of the red imported fire ant, Solenopsis invicta Buren.

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An experimental procedure was developed to study the association of selected bacteria and macroinvertebrates and their response to free available chlorine disinfection. The organisms selected for study were Escherichia coli (LacZ545), Enterobacter cloacae (ATCC 23355), and the amphipod Hyalella azteca. E. coli was shown to bind tightly (1.6 x 104 CFU per amphipod) to this macroinvertebrate and to resist repeated attempts to wash it off. E. cloacae was shown to bind much less tightly (1.4 x 103 CFU per amphipod) to H. azteca and was less resistant to removal by washing. The extent of association is a function of macroinvertebrate size (surface area), but the procedure produces repeatable results usable for controlled experimentation. This method, together with the dual bacterial identification criteria (morphology and antibiotic resistance), was used to study the response of unassociated and associated E. coli and E. cloacae to disinfection with free available chlorine at 1.0 mg/liter. Unassociated E. coli populations decreased to less than 1% of their zero time controls within 1 min of contact time, whereas more than 2% of the associated E. coli populations remained viable after 60 min of contact at 1.0 mg of free available chlorine per liter. Unassociated E. cloacae populations decreased to less than 1% of their zero time controls within 1 min of contact time, whereas ca. 15% of the associated E. cloacae populations remained viable after 60 min of contact at 1.0 mg of free available chlorine per liter. With minor modifications this method can be used to study essentially any combination of bacterium and macroinvertebrate and to thereby ascertain whether a macroinvertebrate can serve to breach the chlorine disinfection barrier, protect potential bacterial pathogens from disinfection, and possibly allow for subsequent pathogen multiplication within a potable water distribution system. One persistent problem associated with current drinking water resources is the infestation of both filtered and unfiltered water supplies and distribution systems by representatives of several taxonomic groups of meioand macroinvertebrates. These groups include Crustacea, Nematoda, Platyhelminthes, and Insecta. Their presence in potable water distribution systems is also expected, but it should not be tolerated. Macroinvertebrates can be the cause of tastes, odors, water discoloration, filter clogging, high turbidity, and political embarrassment. MacKenthun and Keup (16) stated that none of these organisms found in surface waters used for domestic purposes were injurious to health. No reference was cited to substantiate their conclusions. Haney (11) reported that macroinvertebrates (nematodes, in this case) can pose a threat to the public health, particularly if they are exposed to potential pathogens. In their concise