The Effect of Salinity on Tire Leachate Toxicity

Abstract

Previous whole animal bioassays with scrap tireleachates demonstrated an antagonistic interactionbetween salinity and toxicity, but it is unknown ifthe effect is due to an interaction between saltsand toxic mode of action, or release of toxicantsfrom the rubber matrix. Microtox® bacterialluminescence bioassays were performed on tireleachate solutions in a gradient of salinities from0 to 25 ppt to assess salt/toxicant interactions.Leachate solutions generated at specific salinitieswere amended to higher salinities to assess theeffect of sea salt on toxicity vsleachability/solubility of toxicants. Salineleachate solutions were also diluted with freshwaterleachate. Original leachates and samples amendedwith additional salt were aged for 8 days andretested to assess longer term interactions betweensalt and toxicants. The toxicity of leachatesdecreased with increasing salinity up to 15 ppt,with no significant change at higher salinities.Adding sea salt to leachate solutions did notimmediately decrease toxicity significantly, exceptfor samples starting at zero salinity. This wasinterpreted as an indication of interaction betweensea salt and the toxic constituent(s) in theleachate. Salinity decreases also indicated a directeffect of sea salt on toxicants. Ageing samplesindicated a long term interaction between sea saltand leachate toxicants, but not degradation, over atleast a two week period. Tire leachates are probablya greater threat to freshwater habitats thanbrackish or marine habitats, but bioaccumulation ofpersistent organic contaminants from tires is an unknown.