USEPA METHOD 1622

摘要

Problems with the Information Collection Rule (ICR) method for determining concentrations of Cryptosporidium oocysts and Giardia cysts in water are well documented. They include low and highly variable recoveries, high false-positive and -negative rates, and poor precision and accuracy. The method is also technically difficult. To develop regulations ,the US Environmental Protection Agency (USEPA) needs accurate information on the occurrence of protozoa in US source water. The inability to gather this information during the ICR led to development of an alternative method for analysis of Cryptosporidium. Method 1622 was developed and validated for use in the supplemental surveys, which USEPA hopes will provide reliable data on Cryptosporidium occurrence in US source water. Method 1622 is a significant improvement over the ICR method. In this two-laboratory validation, the overall recovery of method 1622 is about 35 percent with a 100-oocyst spike dosage. No nondetects were reported in the 32 natural samples analyzed, and the entire 10-L sample was analyzed on a single well slide. Elimination of subsample analysis on method 1622 reduces the possibility of uneven oocyst recovery that can lead to over-or underestimation of total numbers in a sample. USEPA's 13-laboratory round-robin collaborative trial of method 1622 showed that it is robust, with an overall recovery of 43 percent.