Arsenic and chromium are common toxic elements in drinking water and in the environment. A hybrid anion exchanger (HAIX) uses ferrihydrite, Fe(OH)₃ adsorption and ion exchange to remove the arsenic and chromium from drinking water. These toxic elements do not exist alone, but in a mixture with many dissolved chemical species. Bicarbonate, nitrate and silica are abundant and non-toxic species that have a low affinity for adsorption, but may affect how arsenic and chromium are removed from water. The increased concentration of a mixture of dissolved silica, nitrate and bicarbonate caused earlier breakthrough of arsenic and chromium in a column of HAIX. The earlier breakthrough lowered the amounts of arsenic and chromium removed by the HAIX. The difference between the experimental column results and the adsorption model results shows the amounts of chromium and arsenic removed that are attributable to mechanisms other than surface complexation on ferrihydrite.