# Key Properties for the Toxicity Classification of Chemicals:
## 4 Chemical's Toxicity Assessment Studies Aligned with Regulatory Requirements
### Ecotoxicological Information  
REACH provides the necessary guidelines for the classification of chemicals. However, the scientific community, while relying on the REACH proposals, does not only use this type of testing. With the intention of verifying the correlation between the studies marked by the regulation and the trends followed in terms of environmental impact assessment of chemical substances by the scientific community, a bibliographic review was carried out. The results of this review of the literature are shown in the next paragraphs. In Table 2, the distribution between short-term OR acute and long-term or chronic studies is shown. The number of manuscripts of each category published in WOS is quite similar, being a little bite higher for short-term studies with 53% against long-term studies with 47%. Additionally, for short- and long-term studies, aquatic assays predominate over terrestrial and aerial ones. For the short-term and long-term biomodels, several tests are used. If the percentages obtained for short-term and long-term biomodels are analyzed, it is observed that there are no significant differences and that, in general, the type of biomodel in both short and long term tests are practically the same as well as the percentage of each one. The fundamental difference between some tests and others lies in the time of the test and in the end point of each of them. For both cases, the most frequently used biomodels in aquatic medium are: fish, plants, microorganisms, crustaceans, bacteria, algae, mollusks, planktons, amphibians, and protozoos. For terrestrial analysis, the most used biomodels are plants, microorganisms, worms, fungi, and mites. Finally, in the case of aerial quality evaluation, the main biomodels used are birds, bees, salamanders, ferns, and lichens. In the case of aquatic biomodels, fish is the most popular biomodel. This may be justified since fishes are an important link in the aquatic food chain. The most used tests are short term or acute toxicity, by exposition of fish to high concentrations of chemicals during a short period of time (days). Several enzymatic tests, gene expression, toxicity profile, quantification of EC50, bioaccumulative analysis, toxicokinetics study, pathological effects, swimming behavior, or embryo development, among others, are used. Some of species used are: _Danio rerio_[51; 64; 67; 68; 69; 70; 71], _Larimichthys polyactis_[72], _Oreochromis niloticus_[73], _Oryzias melastigma_[74; 75], _Cyprinus carpio_[76; 77], _Poecilia splenops_[78], _Bryconops caudamulatus_[79], _Oreochromis niloticus_[80], _Gasterosteus aculeatus_[81; 82], _Pungitius pungitius_[82], or _Rhamdia quelen_[83] among others. In the case of plants, the most common tests evaluate the effect on growing, biosorption, bioaccumulation, or toxicity. Some typically used species are: _Lemma minor_[84; 85], _Vallisneria natans_[86], _Lepidium sativum_[87; 88], and _Myriophyllum spicatum_[89]. Crustaceans are frequent species worldwide and are used to carry out acute and chronic toxicological tests. In general, the used tests are related to reproduction, immobilization, biomarkers, etc. The most common crustaceans are: _Daphnia magna_[87; 90; 91; 92; 93; 94] and _Artemia salina_[95]. Algae, as plants, are an important part of the aquatic food chain. If this biomodel is altered by a chemical, a negative effect can be observed in other organisms. Algae are preferred to use because their maintenance is easy and they can predict the hazard in sediments or in other biomodels. The most widespread tests are growth inhibition test, measurement of chlorophyll values, or evaluation of several biomarkers that can be used to determine if chemicals can affect the algae community. Some species used are _Chlorella pyrenoidosa_[96] and _Raphidocelis subcapitata_[93; 94; 97; 98]. In the case of bacteria, the most common species used in ecotoxicological studies is _Alliibrio fischeri_[60; 87; 93; 94; 94].