Environmental selenium volatilization is possibly conferred by promiscuous reactions of the sulfur metabolism

Chemosphere, vol. 345, pp. 140548

Abstract

Selenium deficiency affects many million people worldwide and volatilization of biogenically methylated selenium species to the atmosphere may limit Se entering the food chain. However, there is very little systematic data on volatilization at nanomolar concentrations prevalent in pristine natural environments. Pseudomonas tolaasii cultures efficiently methylated Se at these concentrations. Nearly perfect linear correlations between the spiked Se concentrations and Dimethylselenide, Dimethyldiselenide, Dimethylselenylsulfide and 2-hydroxy-3-(methylselanyl)propanoic acid were observed up to 80 nM. The efficiency of methylation increased linearly with increasing initial Se concentration, arguing that the enzymes involved are not constitutive, but methylation proceeds promiscuously via pathways of S methylation. From the ratio of all methylated Se and S species, one can conclude that between 0.30% and 3.48% of atoms were Se promiscuously methylated at such low concentrations. At concentrations higher than 640 nM (∼50 μg/L) a steep increase in methylation and volatilization was observed, which suggested the induction of specific enzymes. Promiscuous methylation at low environmental concentrations calls into question that view that methylated Se in the atmosphere is a result of a purposeful Se metabolism serving detoxification. Rather, the concentrations of methylated Se in the atmosphere may be "coincidental" i.e., determined by the activity of S cycling microorganisms. Further, a steep increase in methylation efficiency when surpassing a certain threshold concentration (here ∼50 μg/L) calls into question that natural methylation can be estimated from high Se spikes in laboratory systems, yet highlights the possibility of using bacterial methylation as an effective remediation strategy for media higher concentrated in Se.

Authors 4

1. Ying Liu Aachen Institute for Environmental Research

   FHNW University of Applied Sciences and Arts Northwestern Switzerland · RWTH Aachen University

   Affiliation as printed

   Institute for Ecopreneurship, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Hofackerstrasse 30, 4132, Muttenz, Switzerland; Institute for Environmental Research, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany

   Institute for Ecopreneurship, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Hofackerstrasse 30, 4132, Muttenz, Switzerland

   Institute for Environmental Research, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany

2. Andreas Schäffer Aachen Institute for Environmental Research

   RWTH Aachen University

   Affiliation as printed

   Institute for Environmental Research, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany

3. Mathieu Martinez

   FHNW University of Applied Sciences and Arts Northwestern Switzerland

   Affiliation as printed

   Institute for Ecopreneurship, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Hofackerstrasse 30, 4132, Muttenz, Switzerland

4. Markus Lenz corresponding

   FHNW University of Applied Sciences and Arts Northwestern Switzerland · Wageningen University & Research

   Affiliation as printed

   Institute for Ecopreneurship, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Hofackerstrasse 30, 4132, Muttenz, Switzerland; Wageningen University, Department of Environmental Technology, Bornse Weilanden 9, 6700 AA, Wageningen, the Netherlands. Electronic address: markus.lenz@fhnw.ch

   Institute for Ecopreneurship, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Hofackerstrasse 30, 4132, Muttenz, Switzerland

   Wageningen University, Department of Environmental Technology, Bornse Weilanden 9, 6700 AA, Wageningen, the Netherlands