**9. Conclusion**

Absorption, translocation, and metabolism of herbicides are dependent upon active ingredient form and sensitivity of the target weed species. There is the need of further disclosure within the scientific community connected to the study of weeds regarding the use of 14C-herbicides on absorption, translocation, and metabolism studies in resistant and susceptible weed, mainly in the Brazilian conditions. In this chapter, a step-by-step methodology was suggested in order to meet this need, including the radiation safety orientation and management of resulting radioactive waste from the studies conducted in the laboratory. Techniques that use 14C such as tracers are extremely useful to study the herbicides behavior in the resistant weed, since the radiometric techniques offer the possibility of accurately determining very small amounts in a relatively short time. However, mechanism of resistance to herbicides in this resistant weed population compared with the susceptible population cannot be due to differential absorption, translocation, or metabolism of herbicide in weed; so other studies are necessary to elucidate the mechanism of herbicide resistance on weed population.
