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 CaC0 3 ), 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. Materials and MethodsAll rubber samples were prepared as sheets by a tire manufacturer. A typical summer tire tread compound formula containing a minimum of components needed to make cured (vulcanized) rubber was prepared as a reference sample (sample 1). Twenty-one samples were then prepared by adding different additives to the reference formulation. Different process and extender oils were added to five samples (samples 2-6), different types of antidegradents (antioxidants and antiozonants) to six samples (samples 7-12), different types of vulcanization accelerators to six samples (samples 13-18), and different fillers/ reinforcing agents to four samples (samples 19-22). Table 1 shows the formulations of the different rubber samples. The rubber sheets were mailed to our laboratory immediately after preparation, leachates of the samples were prepared and toxicity tests performed in six test runs (samples 2-5, 6-9, 10-12, 13-15, 16-18, and 19-22). Rubber from each sample was cut into pieces of approximately 2 · 2 · 2 mm and various amounts of the rubber were then placed in 50-mL Petri dishes and diluted with reconstituted water according to ISO (1996), with a hardness of 250 mg/L as CaCO 3 and pH 8.0, to give...

Acute aquatic toxicity of tire and road wear particles to alga, daphnid, and fish

“…The toxicity of TP in aquatic species has been evaluated and attributed to both inorganic and organic constituents of tires, however, most toxicological studies to date have focused on TP generated from shredded/powdered tire tread or extracts of tire tread (Gualtieri et al 2005a;Henkelmann et al 2001;Wik 2007;Wik andDave 2005, 2006;Zheng et al 2002). Zinc has been identified as an agent causing toxicity in several studies (Gualtieri et al 2005b;Nelson et al 1994;), although the release of zinc from TP has been shown to vary based on surface area (particle size), loading rates, and extraction conditions (Gualtieri et al 2005b).…”

Identification of benzothiazole derivatives and polycyclic aromatic hydrocarbons as aryl hydrocarbon receptor agonists present in tire extracts

“…Tire wear components are present throughout the environment and numerous studies have not only catalogued the specific chemicals leached from these materials, but they have also reported on the toxic and biological consequences of exposure to leachates and extracts of these materials on the aquatic environment and organisms [1–3]. Human exposure to chemicals leached from tires, shredded tires and tire wear material can occur by dermal exposure from the environmental sources and ingestion of contaminated materials as well as inhalation of airborne particulate matter derived from tire wear material [2].…”

“…In addition to the principal ingredient of rubber, tires contain a wide variety of chemicals that contribute to properties such as softness and resistance to skid, rolling, abrasion, aging and others [1,2]. Chemical additives included in the processing of tires to obtain these characteristics include highly aromatic oils (known to contain high concentrations of polycyclic aromatic hydrocarbons [PAHs]), metals, peroxides, benzothiazole (BT) derivatives, phenols, phthalates, aromatic amines, and other chemicals as well as those that are formed during the tire vulcanization process [1–3]. Many of these chemicals are known to be toxic and/or carcinogenic.…”

“…Many of these chemicals are known to be toxic and/or carcinogenic. Considering the number of tires currently used and those that are disposed of, the amount of tire particles on roadways released as a result of road wear, and the increasing and extensive use of shredded or crumb tire in a wide variety of applications, a substantial amount of chemicals can and/or are known to be released from vehicle tire rubber into the environment as a result of weathering and leaching [1–4]. Accordingly, there are significant concerns regarding the environmental and toxicological impact of chemicals that can be released (leached) from car tire rubber during weathering and numerous studies have examined the toxicity of tire leachate (reviewed in Wik and Dave [2]).…”

“…Leachates or extracts of rubber tire have been shown to produce toxicity in a variety of aquatic organisms, including fish, amphibians, invertebrates, bacteria and plants [1,2,5–9], and in human lung cell lines [10]. While acute lethality was the most common effect, mutagenic, teratogenic, growth inhibition, oxidative stress and alterations in estrogen receptor and progesterone receptor-dependent gene expression (i.e., endocrine disrupting activity) have also been reported [11,12].…”