Communication of risks: organization of a methylmercury campaign in the Cree communities of James Bay, Northern Quebec, Canada.

In the James Bay region of Canada, with the advent of extensive hydroelectric development, methylmercury contamination of fish has become a serious problem, having a direct impact on the Cree way of living. In 1982, the Cree Board of Health and Social Services of James Bay implemented a methylmercury exposure surveillance program in all Cree communities. Since that time, it has developed several educational tools on methylmercury contamination, including posters, pamphlets, and a video. In 1993 and 1994, Cree leaders, Community Health Representatives, medical staff, and other selected band members were consulted to identify the needs of the population regarding information on mercury. All questions and comments were listed, and a summary was sent to those consulted to double check the type of information required by the population. This led to the preparation of a brochure on mercury in a question and answer format, as well as creation of posters. The brochure and the posters were published in French, English and Cree and distributed in each community. A radio message was broadcast in all communities, and individual and group meetings were also held. Cree involvement in the mercury information program has been essential to its success.

Human perception of electric fields and ion currents associated with high-voltage DC transmission lines.

The objective of this study was to assess the ability of humans to detect the presence of DC electric field and ion currents. An exposure chamber simulating conditions present in the vicinity of high-voltage DC (HVDC) lines was designed and built for this purpose. In these experiments, the facility was used to expose observers to DC electric fields up to 50 kV/m and ion current densities up to 120 nA/m2. Forty-eight volunteers (25 women and 23 men) between the ages of 18 and 57 years served as observers. Perception of DC fields was examined by using two psychophysical methods: an adaptive staircase procedure and a rating method derived from signal-detection theory. Subjects completed three different series of observations by using each of these methods; one was conducted without ion currents, and the other two involved various combinations of electric fields and ion currents. Overall, subjects were significantly more likely to detect DC fields as the intensity increased. Observers were able to detect the presence of DC fields alone, but only at high intensities; the average threshold was 45 kV/m. Except in the most sensitive individuals, ion current densities up to 60 nA/m2 did not significantly facilitate the detection of DC fields. However, higher ion current densities were associated with a substantial lowering of sensory thresholds in a large majority of observers. Data analysis also revealed large variations in perceptual thresholds among observers. Normative data indicating DC field and ion current intensities that can be detected by 50% of all observers are provided. In addition, for the most sensitive observers, several other detection proportions were derived from the distribution of individual detection capabilities. These data can form the basis for environmental guidelines relating to the design of HVDC lines.