Levels of Hexavalent Chromium, Copper, and Total Hardness in Springs and Underground Water in Zanzibar Island. Asian Journal of Applied Sciences, [S. l.], v. 1, n. 5, 2013. Disponível em: https://www.ajouronline.com/index.php/AJAS/article/view/564. Acesso em: 26 dec. 2025.