In the estimation of human exposures to environmental chemicals, the following systemic errors have been known to occur:
* an ever increasing number of chemicals registered for use and difficulty of regulatory agencies to keep track. Many producers use the term confidential business information to withhold information, so exposure data are per se unavailable  even though under TSCA, the US EPA may as of 2016, review and determine if a company´s claim is valid.
* assessments are difficult to be kept up-to-date;
* underestimates of exposure occur because of inadequate assumptions about human behaviors and co-exposures ;
* evolving or insufficient models of toxicokinetics