Chromium Car

One functional disadvantage of hexavalent chromium plating is low cathode efficiency, which results in bad throwing power. This means it leaves a non-uniform coating, with more on edges and less in inside corners and holes. To overcome this problem the part may be over-plated and ground to size, or auxiliary anodes are used around the hard-to-plate areas.
From a health standpoint, hexavalent chromium is the most toxic form of chromium. In the U.S. it is heavily regulated by the Environmental Protection Agency (EPA); the EPA lists it as a hazardous air pollutant because it is a human carcinogen, a "priority pollutant" under the Clean Water Act, and a "hazardous constituent" under the Resource Conservation and Recovery Act. Due to the low cathodic efficiency and high solution viscosity a mist of water and hexavalent chromium is released from the bath, which is toxic. To control these emissions wet scrubbers are used. The discharge from the wet scrubbers is then treated to precipitate the chromium from the solution, because it cannot be discarded in the waste water.
Maintaining a bath surface tension less than 35 dynes/cm requires frequent cycle of treating the bath by a wetting agent and confirming the effect on surface tension. Traditionally surface tension is measured by a stalagmometer. This method is, however, tedious and suffers from inaccuracy (errors up 22 dynes/cm has been reported), and is dependent on user's experience and capabilities.
Additional toxic waste that is created from hexavalent chromium baths include lead chromates which form in the bath because lead anodes are used. Barium is also used to control the sulfate concentration, which leads to the formation of barium sulfate, a hazardous waste.