Environmental impacts and leachate analysis of waste rubber incorporated in construction and road materials: A review

In recent years, the recycling of waste tyre rubber in construction and road materials has emerged as a potential innovative solution to the growing waste rubber tyre dilemma. However, to determine the feasibility of any recycling method, it is crucial to assess the potential environmental implications of the proposed method. The environmental conditions waste tyre rubber products are exposed to are often not accurately simulated in leachate studies, leading to incomplete findings. The Toxicity Characteristics Leaching Procedure (TCLP) (1997) and Australian Bottle Leaching Procedure (ABLP) (1992), which have been used in most leachate studies in the past, have been criticised for inadequate replication of site conditions when applied to assess the leachability of modified materials. The objective of this study is to (1) review standard leachate testing methods and subsequently investigate the adequacy of these methods, (2) review all available major research focusing on the leaching characteristics and environmental and health implications of products recycled with waste tyre rubber, (3) prepare recommendations for the improvement of future leachate studies and testing based on the assessment of existing research. The existing leachate analysis studies that assess the environmental implications of different applications of waste tyre rubber have demonstrated that considerable knowledge gaps exist in the current body of knowledge. It was found leachate studies involving the recently published ABLP (2019) and Leaching Environmental Assessment Framework (LEAF) (2017) appeared to better replicate local environmental conditions and yield results of higher integrity and precision due to improved testing procedures. This study recommends that the ABLP and LEAF testing methods be applied to assess the leachability of heavy metals and organic materials (on which minimal research has been conducted) of all currently available products incorporated with waste tyre rubber, as well as in future leachate studies of waste tyre rubber.