According to testing conducted by the regulatory agency, melamine ingested through contaminated feed does not accumulate in pork and is filtered out of the body by the action of the kidneys.
The findings bring some relief to the meat industry, which faced the sudden quarantine of around 56,000 swine while an investigation was being carried out.
The animals, which were held on farms in California, North Carolina, South Carolina, New York, Kansas, Utah and Illinois, have now been cleared for processing.
USDA said the testing bolsters the conclusions reached by a human health risk assessment that there is a "very low risk" of human illness from the consumption of meat from animals exposed to contaminated feed.
Announced last week, the risk assessment has now been updated with an examination of a "most extreme risk assessment scenario".
Scientists assumed that all the solid food a person consumes in an entire day contained melamine, and the melamine compound cyanuric acid, at levels potentially present in the meat.
In this scenario, the potential exposure was found to be about 250 times lower than the dose considered safe, said USDA in a joint statement with the US Food and Drug Administration (FDA).
"Translated to consumption levels, this means that a person weighing 132 pounds would have to eat more than 800 pounds per day of pork or other food containing melamine and its compounds to approach a level of consumption that would cause a health concern.
Previously, the agencies reported that the potential exposure was about 2,500 times lower than the safe level."
The agencies' original risk assessment assumed that testing could detect levels of melamine and related compounds as low as 10 parts per billion (ppb) in pork.
The new assessment assumes that testing can detect levels only as low as 50 ppb in pork, "a more conservative assumption", and an even higher level of 100 ppb is assumed in order to account for the potential presence of cyanuric acid, in addition to melamine.
FDA and USDA said they are also in the process of identifying scientific experts who would be charged with reviewing the updated risk assessment.
They will be asked to provide their views to FDA as quickly as possible, with the intent of finalizing the assessment within several weeks.