A real-time cell electronic sensing (RT-CES) system was used for label-free, dynamic measurement of cell responses to cytotoxicants. Cells were grown onto the surfaces of microelectronic sensors, which are comprised of circle-on-line electrode arrays and are integrated into the bottom surfaces of the microtiter plate. Changes in cell status such as cell number, viability, morphology, and adherence were monitored and quantified by detecting sensor electrical impedance. For cell quantification and viability measurement, the data generated on the RT-CES system correlated well with those from the colorimetric (MTT) assay. For cytotoxicity assessment, cells growing on microelectronic sensors were treated with different cytotoxicants, such as arsenic, mercury, and sodium dichromate. The dynamic responses of the cells to the toxicants were continuously monitored by the RT-CES system. On the basis of the IC50 values, the RT-CES system displays an equal sensitivity to the neutral red uptake assay at specific time points. Furthermore, because the RT-CES system provides real-time information regarding the state of cell morphology and adhesion in addition to cell number, we were able to discern a previously unreported effect of arsenic on NIH 3T3 cells prior to cell death. Also, using the RT-CES system, we were able to monitor cytotoxicity effects that occur within a minute of compound addition. Taken together, the RT-CES system allows for real-time, continuous monitoring and quantitative recording of the whole assay process and provides new insight into the cell-toxicant interaction.

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Increasing concerns over the use of wood treated with chromated copper arsenate (CCA) in playground structures arise from potential exposure to arsenic of children playing in these playgrounds. Limited data from previous studies analyzing arsenic levels in sand samples collected from CCA playgrounds are inconsistent and cannot be directly translated to the amount of children’s exposure to arsenic. The objective of this study was to determine the quantitative amounts of arsenic on the hands of children in contact with CCA-treated wood structures or sand in playgrounds. We compared arsenic levels on the hands of 66 children playing in eight CCA playgrounds with levels of arsenic found on the hands of 64 children playing in another eight playgrounds not constructed with CCA-treated wood. The children’s age and duration of playtime were recorded at each playground. After play, children’s hands were washed in a bag containing 150 mL of deionized water. Arsenic levels in the hand-washing water were quantified by inductively coupled plasma mass spectrometry. Our results show that the ages of the children sampled and the duration of play in the playgrounds were similar between the groups of CCA and non-CCA playgrounds. The mean amount of water-soluble arsenic on children’s hands from CCA playgrounds was 0.50 μg (range, 0.0078–3.5 μg). This was significantly higher (p < 0.001) than the mean amount of water-soluble arsenic on children’s hands from non-CCA playgrounds, which was 0.095 μg (range, 0.011–0.41 μg). There was no significant difference in the amount of sand on the children’s hands and the concentration of arsenic in the sand between the CCA and non-CCA groups. The higher values of arsenic on the hands of children playing in the CCA playgrounds are probably due to direct contact with CCA-treated wood. Washing hands after play would reduce the levels of potential exposure because most of the arsenic on children’s hands was washed off with water. The maximum amount of arsenic on children’s hands from the entire group of study participants was < 4 μg, which is lower than the average daily intake of arsenic from water and food.

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Methyl mercury (MeHg) concentrations in macroinvertebrates and fish were compared among five lakes in burned catchments and five reference lakes on the western Canadian Boreal Plain to determine the influence of forest fire on MeHg bioaccumulation. Two years after fire, MeHg concentrations in five of six aquatic taxa were similar in burned and reference lakes. Among a larger set of 12 lakes, MeHg concentrations in biota were negatively correlated with lake water pH, trophic status, and hardness, reflecting a pre-existing gradient in water chemistry. Biomagnification of MeHg (as determined by regression of MeHg concentration on baseline-adjusted δ15N) was negatively correlated with lake water chlorophyll a concentration. A subsequent logging experiment interrupted by fire provided an opportunity to compare pre- and post-fire MeHg concentrations in aquatic biota. Three months after fire, biota MeHg concentrations had decreased by 32%–50%, and lake water ammonium concentrations had increased 11-fold relative to the previous year. In this nutrient-rich setting, fire may lower MeHg concentrations in aquatic biota over the short-term by inducing an increase in lake productivity that dilutes MeHg at the base of the food web.

The water chemistry of the euphotic zone in 12 lakes within burned and reference watersheds on Alberta's Boreal Plain was surveyed two years post-fire. Five burned and four reference lakes were located in the Boreal Foothills (mean elevation = 1048 m) and three reference lakes were situated at lower elevations in the Boreal Mixedwood ecoregion (748 m). Mean dissolved organic carbon (DOC) concentration in lake water from burned watersheds was 1.4-fold higher than in lake water from reference Foothills watersheds, whereas lake colour increased with the area of catchment burned divided by lake volume (r = 0.98). Reference Mixedwood lakes had higher mean total phosphorus (TP, 1.8-fold) and chlorophyll a (chl a; 4.4-fold) concentrations than reference Foothills lakes. Ten additional lakes from a previous study in boreal Alberta were used to further compare water chemistry between ecoregions. Boreal Mixedwood lakes (n = 13) had higher TP (2.3-fold), chl a (3-fold), and Ca2+ + Mg2+ (3.3-fold) concentrations than Boreal Foothills lakes (n = 9). Our data suggest an influence of forest fire on lake chemistry in the Boreal Foothills, and demonstrate the need for an ecoregion approach to detect the impacts of watershed disturbance on the Boreal Plain. Key words: watershed disturbance, forest fire, lake nutrients, lake elevation, phosphorus, chlorophyll a, anions, cations, dissolved organic carbon.

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