The tendency for iron solid surfaces to adsorb arsenic is well-known and has become the basis for several drinking water treatment approaches that remove arsenic. It is reasonable to assume that iron-based solids, such as corrosion deposits present in drinking water distribution systems, have similar adsorptive properties and could therefore concentrate arsenic and potentially re-release it into the distribution system. The arsenic composition of solids collected from drinking water distribution systems (pipe sections and hydrant flush solids), where the waters had measurable amounts of arsenic in their treated water, were determined. The elemental composition and mineralogy of 67 solid samples collected from 15 drinking water utilities located in Ohio (7), Michigan (7), and Indiana (1) were also determined. The arsenic content of these solids ranged from 10 to 13 650 microg of As/g of solid (as high as 1.37 wt %), and the major element of most solids was iron. Significant amounts of arsenic were even found in solids from systems that were exposed to relatively low concentrations of arsenic (<10 microg/L) in the water.

The electrophoretic mobilities (EPMs) of 30 Mycobacterium avium complex organisms were measured. The EPMs of 15 clinical isolates ranged from ؊1.9 to ؊5.0 m cm V ؊1 s ؊1 , and the EPMs of 15 environmental isolates ranged from ؊1.9 to ؊4.6 m cm V ؊1 s ؊1 at pH 7.Nontuberculous mycobacteria (NTM) include Mycobacterium species that are not members of the Mycobacterium tuberculosis complex. Mycobacterium avium, Mycobacterium intracellulare, and MX organisms are NTM, and are included in the Mycobacterium avium complex (MAC). MX organisms are MAC probe positive by the Accuprobe (Gen-Probe, Inc., San Diego, Calif.) or synthetic nucleic acid probe SNAP (Syngene, San Diego, Calif.) nucleic acid probe identification system but M. avium and M. intracellulare probe negative. MAC organisms are considered human pathogens and in recent years have emerged as a major cause of opportunistic infection in AIDS patients and other immune-compromised hosts (3, 6). The most common disseminated bacterial infection in AIDS patients is from MAC organisms and is second only to the AIDS wasting syndrome as the most common cause of death (11).Many of the NTM are free-living saprophytes that have been isolated from numerous environments, such as water, soil, food, and animals. NTM are able to grow, persist, survive, and colonize in drinking water sources and distribution systems (2, 6). One survey of U.S. public drinking water supplies found that NTM were detected in 35% of the samples, suggesting that drinking water may be an important source of human exposure to these organisms (2). MAC organisms have been isolated worldwide from drinking water distribution systems and are believed to be a source of the M. avium organisms infecting immune-compromised hosts (6, 9). In 1999, the U.S. Environmental Protection Agency (USEPA) published the "Drinking Water Contaminant Candidate List" (CCL), which included MAC organisms due to their clinical significance and their occurrence in drinking water (16). The CCL lists chemical and microbial contaminants that will be considered for future regulatory action.The surface properties of Mycobacterium have been studied to provide more information about the composition of the cell surface and catalase heterogeneity. In a collaborative study, the electrophoretic mobilities (EPMs) of catalases of eight BCG mycobacterial strains and three Mycobacterium phlei and five Mycobacterium fortuitum strains and an M. tuberculosis H37Rv strain were determined by polyacrylamide disk electrophoresis (15). The EPMs of cells of Mycobacterium bovis BCG, M. phlei, Mycobacterium smegmatis, and Mycobacterium microti were compared in acetate-barbiturate solutions from pH 2.5 to 9 (10). EPMs of all cells were identical, despite differences in growth medium, cell age, and chemical treatments. The similarities were attributed to common features of the bacterial cell wall structure. The EPMs of M. bovis BCG Tice cells were measured in phosphate-buffered water (ionic strengths of 0.005 to 0.1 M) with a variety of treatments (12). An isoe...