Caroline Wielandt Egemose
Master Thesis - Environmental Engineering - 2020
The change from a linear economy to a circular economy has become even more urgent in the last decades for the construction sector, due to rapid urbanization, increasing population and resource depletion. The sector is one of the largest resource consumers, where the sectorial waste constitutes one-third of all waste products in Europe. However, the reuse and recycling of construction materials also create an issue, since toxic chemicals can be emitted to the environment, which could lead to human health problems such as allergies, reproduction impairment and cancer.
The toxicity impact of building materials can be assessed as the toxicological footprint throughout the value chain of a product or entity providing a service, where all emissions occurring are included, which is a term known as embodied toxicity. Another way to assess the toxicity is by the embedded toxicity, which is a new concept, that have been defined in this thesis as the toxicity contained within a product or entity providing a service. The embedded toxicity only affects the people, who are in contact with the product from when it is created until disposal thereby value chain wise including only the use stage, and therefore the users are primarily affected.
The embedded toxicity in materials, such as concrete, wood, clay, straw, and wood fibreboard, is extracted with Solid Phase Micro Extraction before being analyzed with gas chromatography-mass spectrometry (GC-MS). The emitted chemicals are identified and quantified as the ratio of chemicals present. The human toxicity impact of the chemicals is characterized and presented in Disability-Adjusted Life Years (DALY) per kg emitted substance. The sum of all chemical impacts gives the total embedded toxicity of each material. The embodied human toxicity is modelled in the software OpenLCA 1.10.2 for three levels of building material: 1 kg building material, 1 m3 building component, and 1 m3 complete external wall system. The calculated midpoint results for the human embodied toxicological impact is presented as DALY per level of building material assessed.
The embedded toxicity is highest for wood fibreboard and lowest for wood. However, the life cycle of 1 kg wood has the highest contribution to the embodied human toxicity impact. Six out of 30 identified chemicals could be characterized as having an impact on human toxicity, where the share of characterized chemicals varies between 4 % and 86 % out of 1 kg emitted substance. The embodied toxicity results for singular building materials show the highest toxicity belonging to 1 kg of wood and a negative embodied human toxicity impact for straw and wood fibreboard. The EcoCocon element and the complete external wall system has a higher impact than the concrete component and external wall. Recycling of wood in the EcoCocon element causes negative embodied human toxicity impact, due to avoided production of new materials. Recycling should always be the first choice even if the materials have a large embedded toxicity. Incineration should only be considered if the materials cannot be stripped of contaminants or properly recycled.
The embedded toxicity should logically be lower than embodied toxicity; however, the embodied toxicity can be negative, pointing towards the embedded and embodied toxicity are not relatable in the way they are assessed in this project. The embedded toxicity is a better method for assessing the consumer health-related toxicity of material compared to the embodied toxicity, that possibly accounts for emissions occurring far away from the consumer. Both methods can benefit in the design and production stage of future building materials as well as play a role in the choice of material used for construction to lower the polluting human toxicity across the value chain of materials.