Abstract A preliminary study on a petrochemical harbor as a potential source of polycyclic aromatic hydrocarbons (PAH) to surface sediments of Guajará bay, located in Belém City, Pará State, Brazil, over the last 10 years is presented here. The 16 priority USEPA PAH were identified and quantified. Surface sediment samples, collected at 5 sites in the bay, near Miramar Petrochemical Harbor (TEMIR), were extracted and analyzed by high performance liquid chromatography with a diode array detector. Total PAH concentration ranged from 533.0 to 3123.3 ng g-1 dry weight with a mean concentration of 1091.9 ng g-1. The most contaminated places were those where muddy sediments were found with highest concentrations of organic matter. The priority PAH with low molecular weight represented 54.4% of the total abundance and indicate that the main source of contamination of the sediments was petrogenic, indicative of the relevant contribution of the petrochemical harbor activity to the input of PAH to Guajará bay. However, pyrolytic PAH coming from fuel combustion, household waste combustion and untreated sewage discharge are also potential contamination sources to this environment.

Resumo: O experimento didático objetiva mostrar a importância da validação do método analítico no estudo da química do sulfato no meio ambiente. Apesar do método de determinação de sulfato apresentar linearidade satisfatória, sensibilidade, limite de detecção e quantificação, e precisão em matrizes aquosas, este experimento mostrou que ele tem baixa exatidão para matrizes aquosas complexas, como água de lagoa e de estuário. Assim, o método só é recomendado para determinações em matrizes aquosas com pouca complexidade, como água potável. Os estudantes foram capazes de compreender os conceitos de validação e assimilar a necessidade de certificar a adequação do método químico, o que garante a qualidade dos resultados e, consequentemente, a fidelidade nas conclusões. Além disso, o emprego dos fundamentos de estatística na análise química e a aplicação de software para tratamento dos dados proporcionaram aos alunos a possibilidade de integrar informática à teoria e prática.

Abstract: This instructive experiment aims to show the importance of validation on analytical method in the study of sulfate chemistry in the environment. Even though the method of sulfate determination has pointed out satisfactory linearity, sensitivity, limit of detection and quantification, and precision in aqueous matrices, this experiment showed that it has low accuracy for complex aqueous matrices, such as lagoon and estuary. Therefore, the method is only recommended for aqueous matrices with little complexity, such as drinking water. The students could were able to understand the validation concepts and grasp the importance of certifying the adequacy of the chemical method, which guarantee the quality of the results and consequently accurate conclusions. Furthermore, the use of the fundamentals of statistic in chemical analysis as well as the application of software for data processing provided the students with an opportunity to integrate computer analysis with theory and practice.