# A Human Health Toxicity Assessment of Biogas Engines Regulated and Unregulated Emissions
## 2 Literature Review
### Health Impact Assessment and Risk Assessment  
As previously discussed, the absence of a common emissions standard, e.g., at EU level, is a point of concern for stakeholders because each country can restrict the substances which it considers the most dangerous. However, within the same country, it can happen that local authorities impose limits that differ from the ones fixed at national level. So, the non-uniformity in emissions standards clearly raises worries in the population living closer to these plants. At the same time, the uncertainties reinforce the need for an experimental campaign focused on ICEs emissions (regulated and unregulated) and aiming to compute the human heath damage and provide a clear answer to stakeholders' concerns. To this purpose, in this work, the Health Impact Assessment is adopted for estimating the harmfulness to human health of both types of biogas ICE emissions, regulated and unregulated. The procedure is then integrated with the Risk Assessment for two groups of dangerous substances, PAHs and dioxins and furans, with the aim of evaluating also their carcinogenic hazardous. Despite impact analyses on human health are still in progress and subject to the uncertainties that such complex problems entail, their application to biogas sector is a point of novelty. In addition, as recommended by the technical literature, the use of HIA and RA is the only way to obtain a more reliable evaluation framework [43]. HIA methods estimate the damage caused by an emission as the number of years lost by a population due to disability or early death (disability-adjusted life year--DALY) [44]. These methods can be found within Life Cycle Impact Assessment (LCIA) procedures, which are recognised methods for the assessment of environmental and human health impacts also in the biogas sector. RA methods estimate the dangerousness of a substance, or a class of related substances, by means of relative toxicity coefficients, determined by toxicological techniques [45; 46]. Among the published works, the one presented by [PERSON] et al. [47] evaluates the environmental aspects and energy requirements of a biogas plant through the LCA approach. The assessment considers six environmental impact categories and an energy one. No evaluations of human health impacts are given. [PERSON] et al. [48; 49] performed an HIA on the air surrounding a gasification plant, studying five scenarios. Emissions impacts are estimated according to the emission factors listed in the literature and are divided by day/night and for the four seasons. They introduced the concept of an intake fraction in order to take into account the amount of pollutant inhaled by a population compared to the amount emitted by the plant. This ratio multiplied by the mass emitted by the plant and the human toxicological effect factor provides the impact score expressed in DALY. [PERSON] et al. [50] applied an LCIA technique to study the management of municipal solid waste. They defined six options and highlighted the best one from the point of view of four damage categories. [PERSON] et al. [51] performed an LCIA with the aim of assessing the environmental impacts of biogas plants devoted to electricity production and fed with agricultural bio-products and/or wastes. They compared multiple biogas production techniques and identified their impacts for some impact categories. Basically, LCIA results are useful to policy makers, but may not be particularly significant for other stakeholders (e.g., the inhabitants of the areas surrounding a biogas plant). In fact, a life cycle assessment devoted to the evaluation of the life cycle environmental impacts associated with electricity generation from biogas reveals that the main contributors to the impacts are the production of biomassand the operation of the anaerobic digesesters [51].