removal - this 

"The unusual toxicity of n-hexane (compared with other alkanes) has resulted in the chemical industry switching away from n-hexane in favour of n-heptane where possible."

see  http://www.cdc.gov/niosh/pel88/142-82.html  "the ACGIH concluded that heptane was more acutely toxic than hexane. The ACGIH therefore recommended limits for heptane that are somewhat lower than the limits for the hexane isomers." , also "because NIOSH believes that "it would be incorrect to conclude that the neurotoxic properties ascribed to n-hexane are unique to this compound [n-hexane]. Other alkanes or related chemicals [such as heptane] that are ultimately metabolized to gamma diketone may have similar toxicity"

Unless there is evidence for a switch the above statement seems unlikely, or simply wrong, especially considering the above report.83.100.251.196