The International Agency for Research on Cancer released a report in March 2015 saying glyphosate is "probably carcinogenic", in conflict with many other scientific studies.
In September, the EPA published a paper that said glyphosate is probably not carcinogenic and scheduled a Scientific Advisory Panel meeting for October 18-21, but then the agency postponed it for later this year.
McCarthy told the committee in June that no EPA employees worked on the IARC report. But the Science Committee released two documents that appear to contradict that claim.
Smith said in a letter to McCarthy: "In light of these contradictions, recent actions taken by EPA to further delay the Science Advisory Panel review for glyphosate do not instill confidence that EPA will fairly assess glyphosate based on sound science."
Meanwhile, IARC advised academic experts on one of its review panels not to disclose documents they were asked to release under United States freedom of information laws.
In a letter, officials from IARC cautioned scientists who worked on a review in 2015 of the weedkiller glyphosate against releasing requested material.
IARC's critics say they want the documents to find out more about how IARC reached its conclusion.
Smith's letter to McCarthy added: "It appears that you have been provided with deliberately misleading information to prepare for your testimony before the Committee, which suggests an attempt by EPA staff to provide untruthful and misleading responses to Congress."
It also said: "That your testimony failed to disclose this information demonstrates that you either purposefully attempted to mislead the Committee or that you have been misled by your staff about the role that EPA officials played in the IARC glyphosate review."Meanwhile, chemical giant ChemChina's proposed £35m takeover of Syngenta is delayed until 2017 after the EC decided on another review of the deal linked to competition concerns from the Chinese buyers. Syngenta say discussions are ongoing.