Long-term dynamics of the atrazine mineralization potential in surface and subsurface soil in an agricultural field as a response to atrazine applications

The dynamics of the atrazine mineralization potential in agricultural soil was studied in two soil layers (topsoil and at 35-45 cm depth) in a 3 years field trial to examine the long term response of atrazine mineralizing soil populations to atrazine application and intermittent periods without atrazine and the effect of manure treatment on those processes. In topsoil samples, (14)C-atrazine mineralization lag times decreased after atrazine application and increased with increasing time after atrazine application, suggesting that atrazine application resulted into the proliferation of atrazine mineralizing microbial populations which decayed when atrazine application stopped. Decay rates appeared however much slower than growth rates. Atrazine application also resulted into the increase of the atrazine mineralization potential in deeper layers which was explained by the growth on leached atrazine as measured in soil leachates recovered from that depth. However, no decay was observed during intermittent periods without atrazine application in the deeper soil layer. atzA and trzN gene quantification confirmed partly the growth and decay of the atrazine degrading populations in the soil and suggested that especially trzN bearing populations are the dominant atrazine degrading populations in both topsoil and deeper soil. Manure treatment only improved the atrazine mineralization rate in deeper soil layers. Our results point to the importance of the atrazine application history on a field and suggests that the long term survival of atrazine degrading populations after atrazine application enables them to rapidly proliferate once atrazine is again applied.

Monod kinetics rather than a first-order degradation model explains atrazine fate in soil mini-columns: implications for pesticide fate modelling

Pesticide transport models commonly assume first-order pesticide degradation kinetics for describing reactive transport in soil. This assumption was assessed in mini-column studies with associated batch degradation tests. Soil mini-columns were irrigated with atrazine in two intermittent steps of about 30 days separated by 161 days application of artificial rain water. Atrazine concentration in the effluent peaked to that of the influent concentration after initial break-through but sharply decreased while influx was sustained, suggesting a degradation lag phase. The same pattern was displayed in the second step but peak height and percentage of atrazine recovered in the effluent were lower. A Monod model with biomass decay was successfully calibrated to this data. The model was successfully evaluated against batch degradation data and mini-column experiments at lower flow rate. The study suggested that first-order degradation models may underestimate risk of pesticide leaching if the pesticide degradation potential needs amplification during degradation.

Bone turnover during short-term therapy with methylprednisolone or budesonide in Crohn's disease

BACKGROUND

Glucocorticosteroids are used frequently for the treatment of relapses of Crohn's disease.

AIM

To investigate the influence of the new topically active glucocorticosteroid budesonide in comparison with methylprednisolone on bone turnover in a randomized open trial.

METHODS

Twenty-nine patients received either budesonide (controlled ileal release formulation) 9 mg for 10 weeks, or methylprednisolone 32 mg (equivalent to 40 mg prednisone) orally for 3 weeks with subsequent tapering.

RESULTS

Patients who completed the trial with methylprednisolone (n = 8) had suppression of serum osteocalcin (30.2 +/- 2.6 to 20.4 +/- 2.0 ng/mL. P < 0.01), whereas no changes in this parameter of bone synthesis were observed during budesonide treatment (n = 11) (34.8 +/- 3.1 to 33.0 +/- 3.5 ng/mL). Urinary pyridinolines and deoxypyridinolines, highly sensitive markers of bone degradation, did not change in either group.

CONCLUSION

Short-term methylprednisolone therapy impairs osteoblast activity in patients with Crohn's disease whereas budesonide does not.