Measurement and modelling of organophosphates leaching from concrete to water
(English)Manuscript (preprint) (Other academic)
Organophosphate triesters used as additives in materials are leaching into the environment and have been found as pollutants in both water and sewage samples. Concrete is one of the most commonly used materials in the world and often contains tributyl phosphate (TBP) and triisobutyl phosphate (TiBP) as anti-foaming agents. In the present study, leaching of TBP and TiBP from concrete to water was measured over 16 weeks under laboratory conditions. The release was initially high (TBP 2900 ± 1060 10 μg/m2h; TiBP 8500 ± 800 μg/m2h), and then dropped to a low stable level over a six-week period. A generic model was developed to predict leaching of organic compounds to water. Three types of diffusion were modelled, dissolution from the surface, diffusion in cracks and pores, and diffusion in micro-pores in the concrete. The former type was assessed using the Nernst-Brunner dissolution and Fickian diffusion theory. The latter types required the use of three modules to model diffusion, solubilisation and 15 convective mass transfer processes separately. The boundary layer solubilisation was modelled using the Abraham solubility equation and solvation parameters taken from literature data. The results showed that the initial release of organophosphates from concrete to water can be significant (in some cases, >40% of the additive leaches out over the first few weeks) and that the long-term release of organophosphates from concrete constructions to the surrounding water can be accurately modelled. The model was applied to 20 estimate the release of TiBP to river water from the foundation of a bridge, resulting in a total loss of 2% of the additive over 8 years, with seasonal fluctuations in loss rate following changes in temperature and water flow. Due to the generic nature of the model, it can also be used to assess the leaching of other additives from concrete constructions to aquatic environments.
Chemical Sciences Materials Chemistry
IdentifiersURN: urn:nbn:se:umu:diva-66360OAI: oai:DiVA.org:umu-66360DiVA: diva2:606209