http://en.wikipedia.org/wiki/Cyanide_poisoning
Chronic exposure:
Exposure to lower levels of cyanide over a long period (e.g., after use of cassava roots as a primary food source in tropical Africa) results in increased blood cyanide levels, which can result in weakness and a variety of symptoms, including permanent paralysis, nervous lesions[5][6][7], hypothyroidism[8], and abortions[9][10]. Other effects include mild liver and kidney damages[11][12].
the human liver is capable of metabolizing cyanide quickly in low doses (smokers breathe in hydrogen cyanide, but it is such a small amount and metabolized so fast that it does not accumulate).