Bacterial enzyme based spectrophotometric determination of phthalate esters in drinking water stored in PET bottles
2019
Jayshree, Annamalai | Vasudevan, Namasivayam
Phthalate esters (PEs) are major water pollutants raising concern of endocrine disruption on daily uptake even at nano-gram level. Among PEs, di-(2-ethylhexyl) phthalate (DEHP) is a high molecular weight PE predominently found in most of the plastic and PVC products. In the present study, daily consumption of PET bottle stored drinking water was taken into account; where leaching PEs occurs easily from its supporting matrix. Determination of PEs in water and other environmental samples by conventional methods involves solvent extraction and sophisticated instruments. To overcome such scenario, in the present study enzyme based spectrophotometric determination of PEs is been proposed. Purified bacterial esterase of 38 kDa is used in the study with optimised pH, temperature and T₅₀ as 7.0, 40 °C and 65 °C. The Km and Vmax values of the purified esterase were derived to be 138.88 µM for DEHP as substrate and 3.15 µmol of phthalic acid liberated min⁻¹ mL⁻¹. Inhibitory effect of metals, minerals and salts that are commonly present in water was assessed at two varied concentrations: 10 and 30 ppm. Magnesium, sodium and mercury exhibited maximum inhibition of 41–47% when compared to other inhibitors. In spectrophotometric determination, upon enzymatic reaction of purified esterase with condensed PET bottle stored drinking water, PE concentration was quantified to be 0.01–0.54 µg L⁻¹. LoD and LoQ based on method validation were calculated to be 0.4 and 1.18 µg L⁻¹. Thus, this study would serve to overcome tedious solvent based extraction process and sophisticated instruments in the detection and quantification of PEs.
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