TAPPI TIP 0304-61 attempts to provide a basic understanding of the role that copper plays in a printing ink, its use and its control. Copper is a concern to many box makers since its presence in plant effluents is often monitored by local sewage authorities. Therefore, caution should be exercised as the copper discharge limits in certain municipalities are extremely low. In some cases, these limits are less than 0.0001% (1.0 ppm).