Mulch made from recycled construction and demolition (C&D) wood has been reported to contain chromated copper arsenate (CCA)-treated wood and potentially release arsenic in the leachate by rainfall. Such recycled wood mulch is commonly masked with iron-oxide colorant, which is known to combine with arsenic. The objective of this study was to evaluate the levels of arsenic leaching from C&D recycled wood mulch and potential effects of the colorant on leaching rates. Mulch samples observed were paired (dyed and non-dyed) in three groups [untreated wood, 5 % treated wood, and 100 % treated wood]. The leachates were collected for one year and analyzed for arsenic. Arsenic in the leachate from untreated wood mulch was consistently at low levels (< 3 ~ 13 ug/L). The average concentrations from 5 % treated wood mulch were 341 (non-colored) and 258 μg/L (colored). The average concentrations from 100 % treated wood mulch were 4,490 (non-colored) and 3490 μg/L (colored). For the entire one year monitoring period, the colorant reduced the arsenic concentration by 24 and 29 % for the non-colored 5 % treated wood mulch and 100 % treated wood mulch, respectively. The study showed that recycled C&D wood mulch, which contains small percentages of CCA-treated wood, release significantly large levels of arsenic by rainfall and iron oxide colorant reduces the arsenic leaching rate for a short period.

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