According to WWWJDIC and ALC, 耐性 is used for drug tolerance (e.g., 耐性現象), but 耐容 is used for radiation (e.g. 耐容線量). Based on that, my guess is that 耐性 can be used to express neutral effects like decrease in drug effectiveness, while 耐容 expresses limitations on harm.
Is this a strict distinction? Does the distinction exist at all?