chemical burns throughout the esophagus and gastrointestinal tract that can be followed by nausea and vomiting. If the substance continues through the gastrointestinal tract, it will be poorly absorbed in the intestines followed by excretion in feces. Toxicity has also been tested on aquatic life including Brachydanio rerio (zebra fish) and Daphnia magna (Water flea). Zebra fish showed CTAB toxicity when exposed to 0.3 mg/L for 96 hours, and water fleas showed CTAB toxicity when exposed to 0.03 mg/L for 48 hours. CTAB along with other quaternary ammonium salts have frequently been used in cosmetics at concentrations up to 10%. Cosmetics at that concentration must only be used as rinse-off types such as shampoos. Other leave-on cosmetics are considered only safe at or below 0.25% concentrations. Injections into the body cavity of pregnant mice showed embryotoxic and teratogenic effects. Only teratogenic effects were seen with 10 mg/kg doses, while both effects were seen at 35 mg/kg doses. Oral doses of 50 mg/kg/day showed embryotoxic effects as well. Similar tests were completed by giving rats 10, 20, and 45 mg/kg/day of CTAB in their drinking water for one year. At the 10 and 20 mg/kg/day doses, the rats did not have any toxic symptoms. At the highest dose, the rats began experiencing weight loss. The weight loss in the male rats was attributed to less efficient food conversion. The tests showed no microscopic alterations to the gastrointestinal tract of the rats. Other toxicity tests have been conducted using incubated human skin HaCaT keratinocyte cells. These human cells were incubated with gold nanorods that were synthesized using seed-mediated, surfactant-assisted growth of gold nanoparticles. Gold nanoparticles are shown to be nontoxic, however once the nanoparticles are put through the growth solutions, the newly formed nanorods are highly toxic. This large increase in toxicity is attributed to the CTAB that is used in the growth solutions to cause anisotropic growth. Experiments also showed the toxicity of bulk CTAB and the synthesized gold nanorods to be equivalent. Toxicity tests showed CTAB remaining toxic with concentrations as low as 10 μM. The human cells show CTAB being nontoxic at concentrations less than 1 μM. Without the use of CTAB in this synthesis, the gold nanorods are not stable; they break into nanoparticles or undergo aggregation. The mechanism for cytotoxicity has not been extensively studied, but there has been possible mechanisms proposed. One proposal showed two methods