It's pointing out that the approach that toxicology has taken conventionally refers to the average Canadian. What would their exposures be, and at what exposure would we start to see health effects? This research really is pointing out that each of us at different developmental stages in life goes through these windows of vulnerability at which the threshold for health effects for the average person is really irrelevant, because really low doses might affect us. In utero is such a time, as are puberty, pregnancy, and menopause, where there would be these different windows of vulnerability at which a very low dose might have a much bigger effect, either later in that person's life or more immediately.
On June 9th, 2016. See this statement in context.