Quantitative analyses to estimate the bioaccessibility of a hydrolytically degradable cationic flocculant

Poly(lactic acid) choline iodide ester methacrylate, poly(PLA₄ChMA), is a cationic degradable polymer that can flocculate particles and dewater oil sands from tailings ponds. This novel material has yet to be characterized in terms of environmental and human health. If ingested, this substance may become bioaccessible. The bioaccessibility (bioaccessible fraction) of an ingested contaminant is a measure of the portion of an ingested dose that solubilizes and may be available for systemic absorption. In the present study, the partially degraded flocculant and its degradation products, modelled using lactic acid and choline chloride, were subjected to a modified physiologically based extraction test (PBET). Bioaccessible fractions were estimated by proton nuclear magnetic resonance (¹H-NMR) spectroscopy and by high-performance liquid chromatography (HPLC). The measured bioaccessibility of lactic acid in gastric solution containing choline chloride is ∼100% but slightly dropped to 94% in intestinal solution at a solid-to-liquid ratio of 1:200. The partially degraded poly(PLA₄ChMA) did not degrade further during the PBET and is not solubilized (i.e., 0% bioaccessibility) in the gastric phase but is fully solubilized (i.e., 100% bioaccessibility) in the intestinal phase. At the end of PBET intestinal digestion, the molar ratio of lactic acid to choline chloride in the presence of degraded poly(PLA₄ChMA) was 2, approximately the same as in the initial solution. Thus, lactic acid and choline chloride are solubilized to the same extents in both gastric and intestinal solutions. Results suggest that HPLC can be used to directly estimate the bioaccessibility of lactic acid, whereas ¹H - NMR may be used to indirectly quantify the bioaccessibility of both lactic acid and choline chloride by determining their molar ratio in PBET extracts. In future works, these findings may be applied to the estimation of risks from exposure to poly(PLA₄ChMA) as well as to the remediation of contaminants flocculated by poly(PLA₄ChMA) in tailings ponds and in other wastewaters.