Comparison of methods for determining Escherichia coli concentrations in recreational waters

Seventy water samples were collected from three Lake Erie beaches to compar e recoveries of Escherichia coli (E. coli) using the USEPA-recommended meth od for recreational waters (mTEC) to recoveries using three alternative met hods (MI, modified mTEC, and Colilert). Statistical tests showed no differe nces in recoveries of E. coli between hi I and mTEC: however, statistically -significant differences were found between modified mTEC or Colilert and m TEC. The MI agar method provided the most similar assessment of recreationa l water quality to mTEC among the three alternative methods tested. The ran ge of differences between Colilert and mTEC was widest among the three alte rnative methods. In a sample group with a range of values near the single-s ample bathing-water standard, recoveries of E. coli were statistically lowe r using modified mTEC than mTEC; however, MI and Colilert compared well to mTEC in this range. Because samples were collected in a small geographic ar ea, more work is necessary to test within-method variability of the modifie d mTEC, MI and Colilert methods and to evaluate these methods as substitute s for the mTEC method in a variety of recreational waters. Published by Els evier Science Ltd.