3.4.1. Eco-Indicator 99

The Eco-indicator 99 method (EI99) is a representative of the endpoint methods for environmental impact modeling and assessment. The characterization process defines the environment through the perspective of three main categories of damage, also referred to as environmental damage endpoints: Human Health, Ecosystem Quality, and Resources, which are further described by 11 impact points. The results from the EI99 analysis of impact points are subject to further processing—normalizing, grouping and weighting to obtain a single-score indicator, expressed in Eco-indicator points (Pt). The scale is adjusted so that one point reflects one-thousandth of the annual environmental load of an average European inhabitant [49].

Human health, one of the three damage categories recognized in the EI99 method, distinguishes five effects: climate change, ozone layer depletion, carcinogenic effect, respiratory involvement, and ionizing radiation. Deciding on an indicator of the impact area from among the endpoints of the environmental mechanism enables one to define a common unit for all adverse effects to human health. Environmental damage can be responsible for a number of disorders, which is why it requires certain means for the quantification of differences between them, hence the DALY scale. Disability Adjusted Life Years (DALY) assigns binary weights to diseases, where 0 denotes ideal health and 1 death. DALY is derived from the number of year life lost due to premature death or the number of years lived disabled [49–51].

Damage to ecosystem quality is significantly more diverse and less homogeneous compared to the impact on human health. It is expressed as the loss of certain species in a given area. Currently, a temporary solution is in use that allows converting between PAF (Potentially Affected Fraction) and PDF (Potentially Disappeared Fraction) units. This method cuts off and limits the considered groups of species because, theoretically, all species could be in danger of extinction. Three impact categories are considered in damage to ecosystem quality: ecotoxicity, acidification/eutrophication, and land use [30].

Modeling within the third area of ecological burden, resources, involves resource and damage analysis. Eco-indicator 99 accounts exclusively for mineral resources and fossil fuels. The quantification of damage pertaining to this category necessitated introducing a special indicator, surplus energy, expressed in MJ, which is analogous to DALY, PAF, and PDF. The higher the surplus energy—being a derivative of the decrease in concentration—the lower the quality of the resource (Figure 4) [50,51].

**Figure 4.** Grouping in Eco-indicator 99. Own work based on [30].

#### 3.4.2. Cumulative Energy Demand (CED)

Cumulative Energy Demand is expressed in MJ-Eq and describes environmental burden through 7 damage categories: 2 non-renewable sources (nuclear energy and fossil fuels) and 5 renewable sources (solar, water, wind, geothermal, and biomass) [52].

### 3.4.3. IPCC

The scientific assessment method developed by the Intergovernmental Panel on Climate Change, Global Warming Potential (IPCC), serves as a quantitative assessment tool for expressing the contribution of particular greenhouse gases (GHG) to the greenhouse effect, relative to carbon dioxide. The time horizon is 20, 100, or 500 years. The total greenhouse effect damage indicator related to CO2 is equal to 1 [49,52].

#### 3.4.4. Interpretation

Life cycle interpretation identifies in quantitative terms the relevance of findings from LCA, specifically, the disaggregation of results obtained at the LCI stage, characterization, normalization, grouping, or weighting, to specific components [30,36]. The data for the analysis were acquired directly from the car tire manufacturer and a recycling company, whereas the remaining data was derived from the SimaPro databases (PréConsultants, Amersfoort, The Netherlands).

A detailed interpretation of the results obtained from the analysis is given in Sections 4 and 5.
