 For example, wastewater from Mexico City that flows north and is used for irrigation in the state of Hidalgo has been linked to congenital birth defects and high levels of gastrointestinal diseases in that state.Beginning in the mid-1980s, the government enacted numerous antipollution policies in Mexico City with varied degrees of success.Measures such as vehicle emissions inspections, the introduction of unleaded gasoline, and the installation of catalytic converters on new vehicles helped reduce pollution generated by trucks and buses.