# Key Properties for the Toxicity Classification of Chemicals:
## 4 Chemical's Toxicity Assessment Studies Aligned with Regulatory Requirements
### Ecotoxicological Information
It is important to consider, when studying sediments, how they interact with the system as well as the deposition and resuspension [152]. Therefore, adsorption and desorption screening are necessary to determine the distribution of a substance in the ecosystem and to estimate the toxicity in sediments. For these tests, the methodology OECD TM 106: Adsorption-desorption using a batch equilibrium method is followed [27]. OECD guides have also developed a method to determine the toxicity of chemicals in the freshwater dipteran of sediments [154]. According to _[PERSON]_ et al. benthic organisms such as algae, bacteria, mollusks, annelids, and nematodes, are the most adequate ones to predict the complexity of toxicity in sediment-water systems [155]. On the other hand, the most widely used bacteria for evaluating the acute toxicity in sediments is the already mentioned _A. fischeri_[156]. It is also common to test on algae or aquatic plants using as endpoints the effect on the photosynthesis process (chlorophyll measurement) or enzymatic inhibition [157]. The species _Entomoneis ch punctuala_[158] has also been used to evaluate acute toxicity. For sublethal toxicity essays, mussels such as _Mytiilus galloprovincialis_[159] or snails such as _Hydrobai ulvae_[160; 161] can also be used. Finally, the most used biomodels for testing air quality are birds followed by bees or lichens. The experimentation in the case of birds is quite complicated since they are constantly moving animals. The most frequent studies analyze the presence of different chemicals in birds and how these substances affect their organs [162; 163]. In the case of bees, the endpoints analyzed are survival, longevity, toxicity, and changes in gut microbiome composition. The most common species are _Apis mellifera_ L. [164; 165; 166] although others such as _Megachile rotundata_[168], _Apis mellifera anatolicaa_[169], or _Bombus impatiens_[170] can be used. Lichens are also important for evaluating air quality because of their sensitivity to various environmental factors and thus several physiological parameters can be used to evaluate environmental damage [171]. However, these studies are limited. Some works evaluate the air concentrations of toxicants and how chemicals can affect these organisms. Some species such as _Parmotrema timotorum_[172; 173; 174; 175], _Lobaria pulmonaria_[176]_ or _Corticolus lichens_[177], and _Leptogium_ sp. _Lichens_[178] are used. To finish the ecotoxicity section, as previously mentioned, it is also important to analyze other types of studies. Biodegradation of a compound is directly related to the persistence of the substance in the environment. These biodegradation studies are usually performed for organic substances [179; 180; 181]. Additionally, other kinds of studies including adsorption/desorption [182; 183] or bioaccumulation [184; 185; 186; 187; 188] studies are carried out. The results of these types of experimentation give an idea of how compounds behave in the environment and, therefore, how they can affect different ecosystems. Adsorption/desorption screening is used to describe the tendency of a substance to bond to a solid (adsorption) and the tendency of a substance to be released into another system (desorption) [189]; the combination of these two is referred to as the sorption potential [190]. The most commonly used parameter to measure the sorption potential is the log Koc (organic-water partition coefficient) [191], which was mentioned previously as an important property to be measured for obtaining information on the environmental behavior of soils. This parameter is normally used together with aquatic toxicity data to predict the hazard potential of a substance in soil/sediment. The most commonly used technique for this screening is the adsorption-desorption method using the batch equilibrium method [27].