The extent of the problem was pointed out at the beginning of 2004 by the European Commission, which in a letter to the Greek authorities demanded that they apply the relevant directive. The Commission stressed that programs to reduce 99 hazardous substances have not been approved, much less implemented. Among the substances are arsenic, PCBs, or polychlorinated biphenyls, and cassiterite (tin oxide). But for improvements in water quality, there is a need for a better and more systematic monitoring of all boreholes and, more generally, drinking water. To deal with natural toxic substances seeping into water, Albanis said, the best thing is to have different water sources and to drill new boreholes. If this is not possible, then systems to clean the water should be set up. Strict measures are needed to protect water catchment areas and all polluting activities within them should be relocated. As for agricultural chemicals, they need to be drastically reduced – in favor of organic cultivation – while the most toxic should be banned. Another interesting proposal, made in the conclusion to the Macedonia-Thrace study, is the use of a mixture of soil, cane and grass to absorb phosphates and nitrates (a method widespread in northern Europe) and thus prevent seepage of agricultural chemicals into ground and surface water.