A bench study was conducted to compare two membrane filter
techniques for their efficiency in recovering fecal coliforms exposed
to selected heavy metals. The effects on recovery by increasing time
and metal concentration were also examined.
The recovery methods employed included the standard membrane
filter technique (S-MF) and a modified membrane filter technique
(M-MF)~ which consisted of a lactose agar overlay and a five-hour
preincubation at 35 C. The heavy metals Cd, Cr, Pb, and Zn were
examined, each at two concentrations, to evaluate their effect on the
recovery of the I. coli test organism, after exposure for 6, 24, and
48 hours.
A statistical analysis of the data found the recoveries obtained
by the M-MF to be significantly greater (.0001 level) than those
of the S-MF, in all cases. Time was also found to significantly effect
recovery, with recoveries decreasing as time increased. A significant
difference was also found between the effects of the heavy metals
tested and the concentrations of metals was likewise found to
significantly effect recovery, with decreased recoveries being
obtained at the high concentration of each metal.
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