Alternative heavy-duty preservatives include creosote and pentachlorophenol. These include pentachlorophenol ("penta") and creosote. After 1980, the use of pentachlorophenol and mercury-based biocides and their derivatives was forbidden. Both hypochlorite and pentachlorophenol have reduced effectiveness at pH values greater than 8. Zinc has showed much higher reactivity toward pentachlorophenol than iron. Prevention treatment with pentachlorophenol failed to inhibit development of fungus. In 1982, EPA amended the regulations with numeric limitations for pentachlorophenol, trichlorophenol and zinc. Pentachlorophenol may be measured in plasma or urine as an index of excessive exposure. Bridges and similar structures such as piers can still be treated with pentachlorophenol. This association was first made when individuals employed in the manufacturing of pentachlorophenol were examined. At the time, this was the largest spill of pentachlorophenol in United States history.