AUTHORS: Domek MJ, LeChevallier MW, Cameron SC, and McFeters GA
PUBLICATION REF: Applied and Enviromental Microbiology 48: 289-293, 1984
PURPOSE OF STUDY:
Although high concentrations of metals are known to cause injury to coliform bacteria, little is known about these effects at the concentrations of metals commonly found in drinking water. This study investigates the effect of low levels of copper on coliform bacteria, specifically Escherichia coli (E. coli.) cells, in samples of typical drinking water.
MATERIALS AND METHODS:
Copper concentrations were determined by the differential pulse polarographic method in 44 drinking water samples drawn from two drinking systems in which chlorine residuals were low. Oxygen uptake levels were also determined.
In the 44 samples tested, copper concentrations ranged from a minimum of 0.007 mg/liter to a maximum of 0.540 mg/liter with a mean of 0.117 mg/liter. A concentration of 0.05 mg/liter produced greater than 90% injury to the E. coli population within 2 days and over 99.5% after 5 days. A higher concentration (0.25 mg/liter) caused injury at a faster rate. Increasing temperature also accelerated the rate of copper-induced injury. Copper alone caused as much injury as a mixture of copper, lead, and cadmium.
Exposure to copper has been shown to cause damage to E. coli in drinking water. Since copper from both natural and man-made sources may be present in drinking water, the effect of copper on coliform bacteria should be considered when testing public water supplies. Injury due to sublethal amounts of copper can lead to underestimation of the bacterial count when m-Endo agar rather than the more sensitive m-T7 medium is used.