France, Oct. 18 -- Dangerous chemicals are contaminating France's water supply at levels far worse than previously known, with dozens of toxic pesticide byproducts going unchecked, an environmental group is warning.

In a report this week, the NGO Generations Futures found that 56 pesticide byproducts known as metabolites - substances formed when chemicals break down - are not being monitored in groundwater or drinking water, despite likely exceeding legal safety limits.

Their analysis, based on research from French health and safety agency, found these metabolites probably contaminate groundwater above the legal limit of 0.1 microgrammes per litre.

The substances can seep into soil, surface water and groundwater before making their way...