title: Conservative tracer bromide inhibits pesticide mineralisation in soil.
abstract: Bromide is a conservative tracer that is often applied with non-conservative solutes such as pesticides to estimate their retardation in the soil. It has been applied in concentrations of up to 250 g Br L-1, levels at which the growth of single-celled organisms can be inhibited. Bromide applications may therefore affect the biodegradation of non-conservative solutes in soil. The present study investigated the effect of potassium bromide (KBr) on the mineralisation of three pesticides - glyphosate, MCPA and metribuzin - in four agricultural A-horizon soils. KBr was added to soil microcosms at concentrations of 0, 0.5, 2.5 and 5 g Br-L-1in the soil solution. The study concluded that KBr had a negative effect on pesticide mineralisation. The inhibitory effect varied depending on the KBr concentration, the type of pesticide and the type of soil. Furthermore, 16 S amplicon sequencing revealed that the KBr treatment generally reduced the abundance of bacteroidetes and proteobacteria on both an RNA and DNA level. Therefore, in order to reduce the effect of KBr on the soil bacterial community and consequently also on xenobiotic degradation, it is recommended that KBr be applied in a concentration that does not exceed 0.5 g Br-L-1in the soil water.
authors.affiliation: Geological Survey of Denmark and Greenland, Department of Geochemistry, Copenhagen, Denmark. Electronic address: tib@geus.dk.
authors.forename: Tina B
authors.initials: TB
authors.lastname: Bech
authors.affiliation: Geological Survey of Denmark and Greenland, Department of Geochemistry, Copenhagen, Denmark.
authors.forename: Annette E
authors.initials: AE
authors.lastname: Rosenbom
authors.affiliation: Novozymes, Copenhagen, Denmark.
authors.forename: Sebastian R
authors.initials: SR
authors.lastname: Sørensen
authors.affiliation: Aarhus University, Department of Environmental Science, Roskilde, Denmark.
authors.forename: Carsten S
authors.initials: CS
authors.lastname: Jacobsen
mesh_terms: D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000378:metabolism; D001673:Biodegradation, Environmental / Q000187:drug effects*; D001965:Bromides / Q000494:pharmacology*; D005998:Glycine / Q000031:analogs & derivatives / Q000378:metabolism; D010575:Pesticides / Q000378:metabolism*; D017680:Potassium Compounds / Q000494:pharmacology*; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism*; D014227:Triazines / Q000378:metabolism; D000097797:Glyphosate
chemical_list: D008456:2-Methyl-4-chlorophenoxyacetic Acid; D001965:Bromides; D005998:Glycine; D010575:Pesticides; D017680:Potassium Compounds; D012987:Soil; D012989:Soil Pollutants; D014227:Triazines; D000097797:Glyphosate; C039004:potassium bromide; C009235:metribuzin