**1. Introduction**

Plastics have been critical in human development. Because of their unique properties including a wide range of temperature use, their resistance to chemicals and light, and their mechanical strength, plastics have brought important advances in health, housing, transportation, science, and education. However, like other man-made materials, when discarded, they accumulate permanently in the natural environment due to their lack of biodegradability. As time goes by and they are exposed to the drag of currents other environmental factors (such as temperature changes, mechanical abrasion, solar irradiation), these polymers break down into microplastics (MPs; 1–5000 m in their longest dimension). The MPs generated in this way are called secondary MPs and are the most abundant type in water bodies [1]. Some MPs are intentionally manufactured for specific applications such as microbeads used in exfoliants or detergents and are called primary MPs [1].

The study of MPs as contaminants began in 2007, and since then many experimental studies have been conducted in which MPs are detected and/or identified. The methodology for the characterization of MPs in water includes sampling, separation from the environmental matrix, quantification, and identification. However, some identification and separation methods work for certain types of MPs while overlooking or damaging others, generating studies that are not comparable with each other and hindering possible solutions such as the estimation of ecological risk assessment (ERA), which can provide the basis for future legislation regarding the use and discharge of MPs.

The ERA is an exposure and dose-response study based on the comparison between the concentration of a chemical of interest found in an ecosystem of interest (in this case water bodies) with the data on the expected effects of this compound for a specific group (flora, fauna, or human). The exposure studies are affected by the lack of standard methods, as described before, as different types and sizes of MPs are collected and identified depending on the used methodology. The dose-response relationship is studied with animal or plant toxicology and then extrapolated for humans with some standard values (see [2]) to obtain a safe concentration level. Quantifying this value is basic for proper risk analysis, and it can be observed linearly and clearly in chemicals since only the species studied and the concentration varies. But for MPs, it is not so simple because there are many other variables that can generate the toxicity of the polymer, such as additives, size, shape, color, and type of the MP. For this reason, toxicological studies are also not standardized and are performed with different types, forms, concentrations, and sizes of MPs as well as different organisms and toxicological endpoints.

Because of the reasons presented above, Gouin et al. [3] identified that the adequate development of an ERA should include the following:


*Microplastics Environmental Risk Assessment: A Review DOI: http://dx.doi.org/10.5772/intechopen.105162*

These key points indicate that standardization and information reporting are essentially the basis of developing an ERA. Therefore, the present review aims to help researchers on plastic pollution in water to observe how the ERAs for MPs have been carried out and improve what other authors have made. Although only eight experimental articles will be analyzed, throughout the paper references to authors proposing a framework for conducting risk analysis for MPs will be found [3–5].

The purpose of the review is to analyze and compare experimental articles that have calculated an environmental risk assessment (ERA) of MPs in a water body. The aspects to be compared are: (a) the criteria used to define a water body as safe or not (PNEC, HI, RI, etc.); (b) which aspects are considered by these criteria; (c) the results of each ERA; (d) the concentration data used in the risk estimation; and finally (e) if the experiments performed comply with the necessary quality in terms of sampling, separation, and identification of MPs in water bodies according to Koelmans et al. [6].
