My source was David Nutt's research group, who were tasked with assessing the effects of alcohol in order to inform public policy in the UK. The toxic limit is not precise, it's variable depending on many factors but I would imagine it's lower than most people would guess, considering the legal status compared to substances that are non-toxic like LSD, heroin, cannabis, psilocybin, etc. Our laws and attitudes to substances often don't make sense, when considering the overall harm that they do.