High levels of heavy metal accumulation in dental calculus of smokers: a pilot inductively coupled plasma mass spectrometry study.

BACKGROUND AND OBJECTIVE: Various trace elements, including toxic heavy metals, may exist in dental calculus. However, the effect of environmental factors on heavy metal composition of dental calculus is unknown. Smoking is a major environmental source for chronic toxic heavy metal exposition. The aim of this study is to compare toxic heavy metal accumulation levels in supragingival dental calculus of smokers and non-smokers. MATERIAL AND METHODS: A total of 29 supragingival dental calculus samples were obtained from non-smoker (n = 14) and smoker (n = 15) individuals. Subjects with a probability of occupational exposure were excluded from the study. Samples were analyzed by inductively coupled plasma mass spectrometry in terms of 26 metals and metalloids, including toxic heavy metals. RESULTS: Toxic heavy metals, arsenic (p < 0.05), cadmium (p < 0.05), lead (p < 0.01), manganese (p < 0.01) and vanadium (p < 0.01) levels were significantly higher in smokers than non-smokers. The levels of other examined elements were similar in both groups (p > 0.05). CONCLUSION: Within the limitations of this study, it can be concluded that the elementary composition of dental calculus may be affected by environmental factors such as tobacco smoke. Therefore, dental calculus may be utilized as a non-invasive diagnostic biological material for monitoring chronic oral heavy metal exposition. However, further studies are required to evaluate its diagnostic potential.

Biodegradation during contaminant transport in porous media: 3. Apparent condition-dependency of growth-related coefficients.

The biodegradation of organic contaminants in the subsurface has become a major focus of attention, in part, due to the tremendous interest in applying in situ biodegradation and natural attenuation approaches for site remediation. The biodegradation and transport of contaminants is influenced by a combination of microbial and physicochemical properties and processes. The purpose of this paper is to investigate the impact of hydrodynamic residence time, substrate concentration, and growth-related factors on the simulation of contaminant biodegradation and transport, with a specific focus on potentially condition-dependent growth coefficients. Two sets of data from miscible-displacement experiments, performed with different residence times and initial solute concentrations, were simulated using a transport model that includes biodegradation described by the Monod nonlinear equations and which incorporates microbial growth and oxygen limitation. Two variations of the model were used, one wherein metabolic lag and cell transport are explicitly accounted for, and one wherein they are not. The magnitude of the maximum specific growth rates obtained from calibration of the column-experiment results using the simpler model exhibits dependency on pore-water velocity and initial substrate concentration (C0) for most cases. Specifically, the magnitude of micron generally increases with increasing pore-water velocity for a specific C0, and increases with decreasing C0 for a specific pore-water velocity. Conversely, use of the model wherein observed lag and cell elution are explicitly accounted for produces growth coefficients that are similar, both to each other and to the batch-measured value. These results illustrate the potential condition-dependency of calibrated coefficients obtained from the use of models that do not account explicitly for all pertinent processes influencing transport of reactive solutes.