METHODS

The water-soluble amount of Cr (VI) was measured after 1 hour extraction in ultrapure water (18.2 MΩ cm resistivity) at room temperature, according to the standard method EN196-10. 22 After solid-liquid separation, the particle-free water solution was directly analyzed by means of the diphenylcarbazide method and spectrophotometry at 540 nm. All samples had concentrations above the limit of detection and all background control samples had concentrations below the limit of detection, which was determined to be

20 μg/L, corresponding to 1 mg/kg Cr (VI) in dry cement. Independent triplicate samples were measured in parallel for each type of cement. Five different types of Honduran, and two different types of Swedish cements (all Portland cements) were tested. The Honduran cements were collected from ARGOS, CENOSA (Holcim Alliance, Jona, Switzerland). HOLCIM is a multinational enterprise and responsible for most cement manufacture in Central America (El Salvador, Honduras, Nicaragua, and Costa Rica). The two Swedish cements were from Cementa and intended for different purposes. Available details about the seven cement types are provided in Table S1, online supporting information). All of them were at least 1 year old and stored dry prior to the testing. In the case of the Swedish cements, the age of the cement meant that the manufacturer did not anymore guarantee a Cr (VI) content below

2 mg/kg.