By Dr. Alexandre Arenzon – 01/09/23
In Brazil, ABNT (Brazilian Association of Technical Standards) defines the main methodologies used in effluent toxicity assessments. Even environmental agencies, such as FEPAM (Rio Grande do Sul State) and CETESB (São Paulo State), require that the effluent toxicity assessments must be carried out according to these standards. The methodologies proposed by ABNT are elaborated, adapted, and reviewed by ABNT’s Special Study Commission for Ecotoxicological Analysis (ABNT/CEE-106). This commission, made up of a group of experts including representatives from universities, laboratories, industries, environmental agencies, and consultants, has been meeting for over 20 years for this purpose.
Among the methodologies developed by ABNT, the NBR 15499 – (Chronic short-term toxicity – Test method with fish) offers the possibility for the use of two species of fish (Pimephales promelas and Danio rerio) for monitoring the chronic toxicity of different types of samples. Effluents, surface/underground water, and chemical substances samples could, until the last review, have their potential chronic toxicity for fish evaluated using any of the two species mentioned in the standard. However, the standard’s original methodology presented different ways of assessing the chronic effects for each of these fish species. For P. promelas, the chronic evaluation considered the effects on the survival and weight growth of the fish exposed to the samples for 7 days. For D. rerio, were exclusively considered the effects on fish survival in the same period. It is important here to mention that, using the D. rerio method it was mandatory the use of different sample dilutions, even when to monitoring surface water samples. Based on the mortalities observed in the different concentrations of the sample, the LC15 (concentration that causes mortality in 15% of the exposed organisms) should be calculated and this would, then, be used to obtain the chronic estimated value. If there was no mortality, the sample was automatically considered non-toxic. Thus, the effects on the fish growth were not considered, as in the tests with P. promelas.
In 2022, when revising this standard, ABNT/CEE-106 made one of the most radical changes to one of its technical standards. After this review (ABNT NBR 15499/2022), the monitoring of chronic toxicity of effluents and surface/groundwater samples can no longer be performed with D. rerio. Based on data published in a scientific article and on discussions during its meetings, the ABNT Commission concluded that, for effluents, surface and/or groundwater, the method could be flawed and generate false negatives. Thus, the method using D. rerio was restricted to samples of chemical substances and, for other types of samples, the fish P. promelas should be used.
Considering that, in Brazil, D. rerio is considered the most used fish species for monitoring toxicity, changing in the standard protocol will require changes in the structure of the laboratories that wish to carry out the analysis. The other species used for this analysis, providers for P. promelas, a North American species used by USEPA for toxicity assessment, are not found commercially in Brazil. Currently, only two Brazilian commercial laboratories perform tests with P. promelas. Thus, laboratories wishing to assess the chronic toxicity of samples of effluents and/or surface/groundwater must implement the breeding of this organism. But what may seem like a problem is actually an advantage. The breeding of P. promelas in the laboratory, in addition to allowing full traceability of the organisms used in the tests, also provides the laboratory with test organisms for carrying out acute toxicity tests with fish.
In this way, based on the fact that the requirements for maintaining the quality certifications of laboratories determine that they use the most current versions of available methodologies, companies that hire these analyzes must pay attention to the results that are being provided.
