Cairo also has many unregistered lead and copper smelters which heavily pollute the city. The results of this has been a permanent haze over the city with particulate matter in the air reaching over three times normal levels. It is estimated that 10,000 to 25,000 people a year in Cairo die due to air pollution-related diseases. Lead has been shown to cause harm to the central nervous system and neurotoxicity particularly in children. In 1995, the first environmental acts were introduced and the situation has seen some improvement with 36 air monitoring stations and emissions tests on cars. Twenty thousand buses have also been commissioned to the city to improve congestion levels, which are very high.