Maternal periodontal disease and risk of preeclampsia: a case-control study

BACKGROUND

We examined whether pregnant women with periodontal disease have an increased risk of preeclampsia, and we empirically evaluated the extent to which associations between periodontal disease and preeclampsia are dependent upon diagnostic criteria used to define periodontal disease operationally.

METHODS

One hundred and fifty preeclampsia cases and one-fifty normotensive controls who delivered a singleton infant at term were enrolled. Periodontal examinations were performed within 48 h after delivery. Participants' periodontal health status was classified, a priori, into four categories according to the extent and severity of periodontal disease. Putative risk factors for periodontal disease and preeclampsia were ascertained during in-person postpartum interviews using a structured questionnaire and by medical record abstraction. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (95% CIs).

RESULTS

No clinically meaningful differences were observed between cases and controls with regard to periodontal parameters. After controlling for known confounders, severe clinical periodontal disease was not associated with an increased risk of preeclampsia (OR = 0.92, 95% CI: 0.26-3.28). In addition, there was no evidence of a linear increase in risk of preeclampsia with increasing severity of periodontal disease (P for trend = 0.65). When different diagnostic criteria previously used in other studies were used, the prevalence of periodontal disease varied substantially. However, the magnitude and direction of associations between periodontal disease and preeclampsia were largely similar regardless of the diagnostic criteria used to define periodontal disease.

CONCLUSIONS

This study provides no convincing evidence that periodontal disease is associated with preeclampsia risk among Thai women.

Investigation of gas production and entrapment in granular iron medium

A method for measuring gas entrapment in granular iron (Fe0) was developed and used to estimate the impact of gas production on porosity loss during the treatment of a high NO3- groundwater (up to approximately 10 mM). Over the 400-d study period the trapped gas in laboratory columns was small, with a maximum measured at 1.3% pore volume. Low levels of dissolved H2(g) were measured (up to 0.07+/-0.02 M). Free moving gas bubbles were not observed. Thus, porosity loss, which was determined by tracer tests to be 25-30%, is not accounted for by residual gas trapped in the iron. The removal of aqueous species (i.e., NO3-, Ca, and carbonate alkalinity) indicates that mineral precipitation contributed more significantly to porosity loss than did the trapped gases. Using the stoichiometric reactions between Fe0 and NO3-, an average corrosion rate of 1.7 mmol kg-1 d-1 was derived for the test granular iron. This rate is 10 times greater than Fe0 oxidation by H2O alone, based on H2 gas production. NO3- ion rather than H2O was the major oxidant in the groundwater in the absence of molecular O2. The N-mass balance [e.g., N2g and NH4+ and NO3-] suggests that abiotic reduction of NO3- dominated at the start of Fe0 treatment, whereas N2 production became more important once the microbial activity began. These laboratory results closely predict N2 gas production in a separated large column experiment that was operated for approximately 2 yr in the field, where a maximum of approximately 600 ml d-1 gas volumes was detected, of which 99.5% (v/v) was N2. We conclude that NO3- suppressed the production of H2(g) by competing with water for Fe0 oxidation, especially at the beginning of water treatment when Fe0 is highly reactive. Depends on the groundwater composition, gas venting may be necessary in maintaining PRB performance in the field.

Preferential flow path development and its influence on long-term PRB performance: column study

The operating life of an Fe(0)-based permeable reactive barrier (PRB) is limited due to chemical reactions of Fe(0) in groundwater. The relative contributions from mineral precipitation, gas production, and microbial activity to the degradation of PRB performance have been uncertain. In this controlled field study, nitrate-rich, site groundwater was treated by Fe(0) in large-volume, flow-through columns to monitor the changes in chemical and hydraulic parameters over time. Tracer tests showed a close relationship between hydraulic residence time and pH measurements. The ionic profiles suggest that mineral precipitation and accumulation is the primary mechanism for pore clogging around the inlet of the column. Accumulated N(2) gas generated by biotic processes also affected the hydraulics although the effects were secondary to that of mineral precipitation. Quantitative estimates indicate a porosity reduction of up to 45.3% near the column inlet over 72 days of operation under accelerated flow conditions. According to this study, preferential flow through a PRB at a site with similar groundwater chemistry should be detected over approximately 1 year of operation. During the early operation of a PRB, pH is a key indicator for monitoring the change in hydraulic residence time resulting from heterogeneity development. If the surrounding native material is more conductive than the clogged Fe-media, groundwater bypass may render the PRB ineffective for treating contaminated groundwater.