Evaluating bottle liquid-liquid extraction technique for monitoring residual levels of organochlorine pesticides in wastewater treatment-associated matrices
Nikoo F. Afifiyan, Oma Soto, Khoi Phan, Lin Li, Tom Juma, Ochan Otim
Abstract
The gold standard for recovering residual organochlorine pesticides from wastewater and other environmental matrices is the continuous liquid-liquid extraction (CLLE) technique that requires toxic CH2Cl2 as solvent at its refluxing temperature. In light of a recent USEPA proposed prohibitions and workplace protections for CH2Cl2 due to its toxicity, and the fact that CLLE is performed in expensive and currently hard-to-acquire glassware, an alternative to CLLE as currently practiced is therefore needed. The bottle liquid-liquid extraction (BLLE) technique, demonstrated for extracting semi-volatile organic contaminants from surface water, is potentially a low cost and high throughput technique for such recovery. BLLE is cheaper, contains toxic vapor within, and has a smaller laboratory footprint. The technique, performed in a tightly capped bottle, also requires less solvent and is performed at ambient temperature. The latter means less vapor is encountered in the workplace. In this study, BLLE was performed directly in 1-L amber sampling bottles and is shown to recover 21 organochlorine pesticides as efficiently as CLLE from influents and effluents of two wastewater treatment plants, and that CLLE and BLLE can be used interchangeably. No statistical differences were found between CLLE (mean = 77.4, SD = 9.28) and BLLE (mean = 79.1, SD = 14.3); t(22) = 0.548, p(same mean) = .58 even though CLLE recovered more pesticides than BLLE by 5.18 ± 8.15%. This systematic bias fits the expression BLLE = 1.4[CLLE] – 35 (r = 0.88). Both CLLE and BLLE recoveries were consistently higher for 4,4′-DDD and lower for aldrin, heptachlor and endrin aldehyde. Diethyl ether addition, as some suggested, did not improve BLLE. Synopsis: There is need to find a cheap, reliable and high throughput technique for purifying SVOCs from aqueous environmental media efficiently. BLLE, a little known technique, fulfils this need.