Evaluation of optical brightener photodecay characteristics for detection of human fecal contamination

Detection of optical brighteners by fluorometry combined with ultraviolet light (UV) exposure has been proposed as an inexpensive method for detection of human fecal contamination, but has received limited testing. This study evaluated the approach in southern California by applying it to a variety of detergents, sewage and septage samples from the region, as well as to natural stream water as a negative control. The concept of using UV exposure to differentiate fluorescence from natural organic matter proved valid, as the method produced no false positives. However, the method failed to detect half of the detergents tested in natural stream water at 5 μL/L, due to its conservative thresholds. This study identified a method modification that provides greater sensitivity by taking advantage of differences in the shape of photodecay curves between optical brighteners and natural organic matter. This method modification resulted in detection of all detergents, sewage at 1:10 dilution and septage at 1:100 dilution. Several caveats for its use remain, including our observation that the optical brightener signal degraded rapidly in strong sunlight. Additionally, there was low sensitivity for some environmentally friendly detergents, which does not present a problem on a community basis where a mix of detergents are used, but could be of concern for assessing septic inputs from individual homes. Still, the method is simple to employ in the field, yields rapid results and is useful as a low-cost initial screening tool.