Toxic components leaching from tire rubber

Abstract

Tire rubber is a complex mixture of a variety of chemicals, e.g., rubber polymers, carbon blacks, silicas, process and extender oils, vulcanization chemicals, and chemical antidegradents (Barbin and Rodgers, 1994). Leachates of tire rubber are toxic to a range of aquatic organisms; see for example the review by Evans (1997). Attempts made so far to identify the components causing the toxicity of rubber leachates have focused on chemical fractionation and characterization followed by toxicity testing of different fractions. Toxicity identification evaluations of leachates from tire plugs leached in deionized water have indicated that zinc was the main cause of toxicity to Ceriodaphnia dubia (Nelson et al., 1994). Microtox toxicity was caused by several organic compounds spread through a range of polarities (Anthony et al., 1995). A toxicity identification evaluation on leachates obtained from tire wear material leached in reconstituted water (pH 8, hardness 250 mg/L as CaC03), identified nonpolar organic compounds as the main cause of toxicity to Daphnia magna (Wik and Dave, 2006). In this previous study, we also found large differences in toxicity between different tires, which implies that the environmental impact of tire wear can be effectively reduced through rubber formulation if the most toxic components are identified. The aim of this study was to identify the components in tire rubber that are toxic to Daphnia magna, using a novel approach. Rubber formulations containing different additives were produced, and water leachates from the rubber samples were prepared and tested for toxicity using a standardized toxicity test. The main objective of this study was therefore to assess the toxicity to Daphnia magna of different rubber formulations in order to identify the most toxic tire leachate components.