This is an article in which we will be discussing the chemistry of bitumen emulsion from a health, safety, and environmental perspective. GRT poses the question – Is bitumen emulsion safe to use in dust and erosion control? It is important to interrogate the life cycle of products used in dust and erosion control which starts by questioning the cradle-to-cradle journey of bitumen emulsion from crude oil to application in dust and erosion control. To understand and fixate on the matter at hand we first need to understand what exactly bitumen emulsion is. But wait, the key word is bitumen so maybe we need to rewind and understand first what bitumen is. Indeed, without understanding the fingerprint of a material we might get oblivious of its post-use effect which we strongly believe is the case to those blindly using bitumen emulsion for dust and erosion control. Let us partake on the journey to understand but also to challenge the resurgence in use of bitumen emulsions in dust and erosion control in Australia.
Bitumen is a by-product of fractional distillation of crude oil in the refining process. That statement alone introduces a lot of variables. The source of crude and refining technology plays a huge role in the type of bitumen that is obtained from the barrel. The combination of bitumen with water in the presence of a surfactant yields what we then call bitumen emulsion. Depending on the nature of surfactant which can be anionic, cationic, zwitterionic and non-ionic the emulsion bears the name of the surfactant used. For example, a cationic emulsion is a bitumen emulsion formulated from bitumen, water in the presence of a cationic surfactant. The chemistry looks straightforward but there is more to it because the fingerprint from the crude oil and the refining technology increases the potential of carcinogenic hydrocarbons which remain active even when used as bitumen emulsion more so with the presence of water, making it much more dangerous than expected. Okay, lets dissect this topic more by looking at why bitumen emulsion is a concern.
Why is bitumen emulsion a concern?
The chemical fingerprint of bitumen consist of saturates, aromatics, resins as the maltene fraction and asphaltenes. Saturates are mainly branched and long with aliphatic chains and traces of heteroatoms and few crystalline n-alkanes. Aromatics have dominant chemical structures slightly aliphatic in nature and a carbon skeleton with lightly condensed aromatic rings. Resins are polar peptizers that act as dispersing agents for asphaltenes and are made up of 2-4 fused rings. Asphaltenes possess condensed polycyclic aromatic rings which are known to be carcinogenic and traces of transition metals nickel, vanadium, and iron in the form of metallo-porphyrins. The rich chemistry that bitumen possesses is what it brings to the bitumen emulsion by product. The variation in chemical compounds creates short-term and long-term hazards depending on the mode of contact. Potential modes of contact in humans when bitumen emulsion is used is during handling and spraying when it is dispersed onto the surface. Solubility of bitumen chemical constituents in water because of the presence of the surfactant makes it susceptible to leaching and runoff which affects aquatic flora and fauna. The concerns are then further aggregated into environmental and WSH in the text that follows.
What are the environmental effects of bitumen emulsion?
Bitumen consists of different hydrocarbons that have a range of aqueous solubilities. The inherent mobility of these compounds present toxicity to surface water and ground water systems. Research shows that toxicity in early-stage development of fish is linked to concentration of 3-5 ringed alkyl polycyclic aromatic hydrocarbons, metals, and naphthenic acids in bitumen. Degradation chemistry of naphthenic acids is rapid given the presence of unsaturation and cyclization and its by-products have a very short half-life in water. Acute toxicity in diluted bitumen, in the form of bitumen emulsion is strongly associated with lower molecular weight hydrocarbons, naphthalene, alkyl naphthalene and short chain alkanes. Chronic toxicity on the other hand is related to polycyclic aromatic hydrocarbons and alkyl polyaromatic hydrocarbons. There is a lot of chemistry that is seldom paid attention to. For all we know the chemistry of bitumen is very complex so why risk with facts of the knowns even daring to play with the unknowns. It is dangerous and risky to use bitumen emulsions and we will continue to provide evidence WHY?
Hydrophilicity of alky-polyaromatic hydrocarbons relative to their unsubstituted counterparts leads to more accumulation in aquatic and terrestrial flora. Factually, solubility of compounds that result in chronic toxicity is reported low but post use and over time continued residence in water affects fish negatively. Accumulation of polyaromatic cyclic hydrocarbons in fish and aquatic species leads to distortion of the lipid membrane’s structure and function. The 3-5 ringed alkyl polycyclic aromatic hydrocarbons seem to be the most toxic in fish leading to embryotoxicity. In amphibians such as frogs, lower mitochondrial oxygen consumption signals toxicity from polyaromatic hydrocarbons whereas in birds impaired lipid homeostasis is observed. The extend of bioaccumulation vary depending on volume of bitumen emulsion exposed and the metabolic capacity of biotransformation varies from one species to the next. From a formulation perspective bitumen emulsion is an engineered product for cold mix applications. The mechanisms of water loss depend on a lot of factors and the residual bitumen has much more mobility given its presence in solution. In soil and sediments, di- and tri-atomic compounds of lower molecular weight tend to be volatile even when bound therefore their release into water bodies is very easy. Coating of aquatic macrophytes impairs photosynthesis by blocking light. Coating of shoots can block gaseous exchange and coated leaves may lead to occlusion of stomata which prevents carbon dioxide uptake as well as release of transpiration water vapor.
What are the WHS concerns of using bitumen emulsion?
Polyaromatic cyclic hydrocarbons are complicated because they are inevitably found as complex mixtures with other contaminants and photo-transformed products. The functional groups naturally occurring in bitumen which is entirely depend on the parent crude source include polynuclear aromatics, benzene, ethylbenzene, xylene, 2-quinolone type, pyridinic, phenolic and sulfide. Blood samples have revealed a spike in oxidative DNA damage in bitumen exposed workers. Metabolites of polyaromatic hydrocarbons mono-oxygenation are often very highly reactive and more toxic than the parent compound and are related to chemically induced cancers and oxidative stress in vertebrates. Metabolism can be associated with harm. Predominantly enzymes producing unstable and reactive metabolites include oxygenases, epoxide hydrolases, peroxidases, and aldo-keto reductases. Most of these metabolites include reactive oxygen species, diol-epoxides, o-quinone derivatives, phenolic derivatives, and benzylic alcohols. Many benefits have been credited to use of bitumen emulsions with omission of the mention of the effects of toxic polyaromatic hydrocarbon precursors over a duration of time. The high volatility of benzene, toluene, ethylbenzene, and xylene found in bitumen emulsion pose health risk to workers working with it over a prolonged period. In conclusion, we openly answer the question – Is Bitumen Emulsions Safe to Use for Erosion and Dust Control by saying “NO” it is not safe. The use of bitumen emulsion in dust and erosion control should be stopped for human health and environmental reasons.
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