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J Hazard Mater. 2019 Feb 15;364:600-607. doi: 10.1016/j.jhazmat.2018.10.050. Epub 2018 Nov 1.

Biodegradability and toxicity of monorhamnolipid biosurfactant diastereomers.

Author information

1
Department of Soil, Water and Environmental Science, The University of Arizona, Tucson, AZ, 85721, USA.
2
Department of Pharmacology and Toxicology, The University of Arizona, Tucson, AZ, 85721, USA.
3
Department of Chemical and Environmental Engineering, The University of Arizona, Tucson, AZ, 85721, USA.
4
Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ, 85721, USA.
5
Department of Environmental and Molecular Toxicology, Oregon State University, 1007 Agriculture & Life Sciences Building, Corvallis, OR 97331, USA.
6
Department of Soil, Water and Environmental Science, The University of Arizona, Tucson, AZ, 85721, USA. Electronic address: rmaier@ag.arizona.edu.

Abstract

Synthetic monorhamnolipids differ from biologically produced material because they are produced as single congeners, depending on the β-hydroxyalkanoic acid used during synthesis. Each congener is produced as one of four possible diastereomers resulting from two chiral centers at the carbinols of the lipid tails [(R,R), (R,S), (S,R) and (S,S)]. We compare the biodegradability (CO2 respirometry), acute toxicity (Microtox assay), embryo toxicity (Zebrafish assay), and cytotoxicity (xCELLigence and MTS assays) of synthetic rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-C10-C10) monorhamnolipids against biosynthesized monorhamnolipid mixtures (bio-mRL). All Rha-C10-C10 diastereomers and bio-mRL were inherently biodegradable ranging from 34 to 92% mineralized. The Microtox assay showed all Rha-C10-C10 diastereomers and bio-mRL are slightly toxic according to the US EPA ecotoxicity categories with 5 min EC50 values ranging from 39.6 to 87.5 μM. The zebrafish assay showed that of 22 developmental endpoints tested, only mortality was observed at 120 h post fertilization; all Rha-C10-C10 diastereomers and bio-mRL caused significant mortality at 640 μM, except the Rha-C10-C10 (R,R) which showed no developmental effects. xCELLigence and MTS showed IC50 values ranging from 103.4 to 191.1 μM for human lung cell line H1299 after 72 h exposure. These data provide key information regarding Rha-C10-C10 diastereomers that is pertinent when considering potential applications.

KEYWORDS:

Biodegradation; Biosurfactant; Rhamnolipid; Stereochemistry; Toxicity

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