Cationic starch increases strength because it binds to the anionic paper fibers, but it must be added in moderation for the same reason.[6] The amount added is usually between ten and thirty pounds per ton. When starch exceeds the amount the fibers can bind to, it causes foaming in the production process as well as decreased retention and drainage.[6] Another problem with adding too much cationic starch is that the effluent has increased biological oxygen demand (BOD) which is an environmental hazard as well as an increased waste expense for paper makers.[5] To make cationic starches more effective the paper can be made at a higher pH. By doing this the fibers tend to become more anionic increasing the affinity to bond to the starch and creating a stronger product.