Optical Brighteners: Sorption Behavior, Detection, Septic System Tracer Applications

Abstract

Laboratory soil column experiments were used to evaluate the optical brighteners (fluorescent whitening agents) Tinopal3 CBS-X (ASTM designation DSBP-1) and Tinopal3 5BM-GX (ASTM designation DASC-4) and the fluorescent dye eosin Y (C.1. 45380) as adsorbing tracers in subsurface systems. In a low organic carbon content glacial outwash sand (foe = 0.0034, 97% sand by weight) the solid-water distribution coefficient (Kd) was determined to be 0.26 cm113/g for Tinopal CBS-X, 0. 78 cm113/g for Tinopal 5BM-GX, and 0.024 cm11 3/g for eosin Y. All three compounds had simple sigmoidal breakthrough curves. Optical brighteners can be detected in direct solution by fluorometry but suffer from interference associated with naturally occurring organic compounds. Unbrightened cotton can be used to qualitatively detect optical brighteners. Polyethersulfone filter media can be used to selectively remove optical brighteners from solution without changing the background fluorescence spectrum. The exposed filter medium can be analyzed as a solid sample in a scanning spectrofluorophotometer. The resulting spectrum can be used to measure the optical brightener concentration in the filtered sample. Polyethersulfone filters can be used to detect optical brighteners in samples collected in and around septic system drain fields at less than 1 ppb Tinopal 5BM-GX equivalent.Funding for this research project was approved by the Minnesota Legislature [ML 1993, Chap. 172, Art. 1, Sec. 14, Subd. 11 (i)] as recommended by the Legislative Commission on Minnesota Resources from the Minnesota Environment and Natural Resources Trust Fund. A graduate student fellowship awarded to the first author by the National Ground Water Association facilitated the column experiment work. The septic system tracer applications portion of this work was made possible by a joint Blue Earth County, Minnesota Soil and Water Conservation District / Minnesota Pollution Control Agency I Federal Emergency Management Administration grant