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The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux.

DeVries SL, Loving M, Li X, Zhang P - Sci Rep (2015)

Bottom Line: Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others.Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses.The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Atmospheric Sciences, City College of New York, 160 Convent Avenue, New York, NY, 10031, USA.

ABSTRACT
Exposure to sub-inhibitory concentrations of antibiotics has been shown to alter the metabolic activity of micro-organisms, but the impact on soil denitrification and N2O production has rarely been reported. In this study, incubation and column transport experiments were conducted on soils exposed to as many as four antibiotics in the ng · kg(-1) range (several orders of magnitude below typical exposure rates) to evaluate the impact of ultralow dose exposure on net nitrate losses and soil N2O flux over time. Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others. Sulfamethoxazole in particular had a stimulatory effect at ultralow doses, an effect also evidenced by a near 17% increase in nitrate removal during column transport. Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses. The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

No MeSH data available.


Related in: MedlinePlus

Box-whisker plot of daily N2O flux (ppm·day−1) in moist soil (40% water filled pore space) treated with 0–1000 ng·kg−1 Narasin.For each dose, 6 replicate samples were analyzed; statistical outliers are shown as asterisks and data that differ significantly from the control are indicated with arrows.
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f3: Box-whisker plot of daily N2O flux (ppm·day−1) in moist soil (40% water filled pore space) treated with 0–1000 ng·kg−1 Narasin.For each dose, 6 replicate samples were analyzed; statistical outliers are shown as asterisks and data that differ significantly from the control are indicated with arrows.

Mentions: Where any changes in denitrification rate or potential in soil and sediment are observed, changes in the flux rate of N2O, a powerful greenhouse gas are also likely. Though at least one previous study has reported a decrease in N2O from mineral soils treated with 1-1000 μg·L−1 SMX5, the opposite effect was observed in moist soils treated with 1-1000 ng·kg−1 NAR. As seen in Fig. 3, the average N2O flux is around 0.1 ppm·day−1 for all antibiotic treatments and the control after only one day of incubation, but on Day 3 a statistically significant dose-response emerged (see Table 3, p = 0.0067). The dose-response observed is nearly linear with N2O flux ranging from 0.1 ppm·day−1 (Control) to approximately 0.4 ppm·day−1 (1000 ng·kg−1). Although NAR was also shown to stimulate nitrate reduction at each of these doses on Day 3 (Table 1), it is unlikely that accelerated denitrification alone accounts for the increase in N2O flux, especially at the highest dose where nitrate losses are 200% of the control but net N2O flux are 300%. Surplus N2O flux may result from either a shift in the N2O:N2 ratio, a mechanism suggested by Hou et al. (2015) whose experiments with 0.05–100 μg·L−1 sulfamethazine in sediment showed an increase in N2O despite inhibited denitrification26, or it may indicate that antibiotics also affect nitrifier-denitrification rates (NH2OH → N2O or NO2− → NO → N2O) in aerobic soils28. To better constrain source of increased N2O flux, future studies would benefit from the use of isotopic tracers that can be used to distinguish between N2O sources28.


The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux.

DeVries SL, Loving M, Li X, Zhang P - Sci Rep (2015)

Box-whisker plot of daily N2O flux (ppm·day−1) in moist soil (40% water filled pore space) treated with 0–1000 ng·kg−1 Narasin.For each dose, 6 replicate samples were analyzed; statistical outliers are shown as asterisks and data that differ significantly from the control are indicated with arrows.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660347&req=5

f3: Box-whisker plot of daily N2O flux (ppm·day−1) in moist soil (40% water filled pore space) treated with 0–1000 ng·kg−1 Narasin.For each dose, 6 replicate samples were analyzed; statistical outliers are shown as asterisks and data that differ significantly from the control are indicated with arrows.
Mentions: Where any changes in denitrification rate or potential in soil and sediment are observed, changes in the flux rate of N2O, a powerful greenhouse gas are also likely. Though at least one previous study has reported a decrease in N2O from mineral soils treated with 1-1000 μg·L−1 SMX5, the opposite effect was observed in moist soils treated with 1-1000 ng·kg−1 NAR. As seen in Fig. 3, the average N2O flux is around 0.1 ppm·day−1 for all antibiotic treatments and the control after only one day of incubation, but on Day 3 a statistically significant dose-response emerged (see Table 3, p = 0.0067). The dose-response observed is nearly linear with N2O flux ranging from 0.1 ppm·day−1 (Control) to approximately 0.4 ppm·day−1 (1000 ng·kg−1). Although NAR was also shown to stimulate nitrate reduction at each of these doses on Day 3 (Table 1), it is unlikely that accelerated denitrification alone accounts for the increase in N2O flux, especially at the highest dose where nitrate losses are 200% of the control but net N2O flux are 300%. Surplus N2O flux may result from either a shift in the N2O:N2 ratio, a mechanism suggested by Hou et al. (2015) whose experiments with 0.05–100 μg·L−1 sulfamethazine in sediment showed an increase in N2O despite inhibited denitrification26, or it may indicate that antibiotics also affect nitrifier-denitrification rates (NH2OH → N2O or NO2− → NO → N2O) in aerobic soils28. To better constrain source of increased N2O flux, future studies would benefit from the use of isotopic tracers that can be used to distinguish between N2O sources28.

Bottom Line: Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others.Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses.The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Atmospheric Sciences, City College of New York, 160 Convent Avenue, New York, NY, 10031, USA.

ABSTRACT
Exposure to sub-inhibitory concentrations of antibiotics has been shown to alter the metabolic activity of micro-organisms, but the impact on soil denitrification and N2O production has rarely been reported. In this study, incubation and column transport experiments were conducted on soils exposed to as many as four antibiotics in the ng · kg(-1) range (several orders of magnitude below typical exposure rates) to evaluate the impact of ultralow dose exposure on net nitrate losses and soil N2O flux over time. Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others. Sulfamethoxazole in particular had a stimulatory effect at ultralow doses, an effect also evidenced by a near 17% increase in nitrate removal during column transport. Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses. The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

No MeSH data available.


Related in: MedlinePlus