Gamma-ray spectra from more than fifty samples of food products available in stores of Buenos Aires city were measured using a germanium detector. We found concentrations of ¹³⁷Cs up to 10 Bq/kg in tea manufactured in Apóstoles, Misiones-Argentina. Further measurements of tea leaves, yerba mate leaves and soils, all coming from a cultivated area in this region, also show the presence of ¹³⁷Cs contamination. Our data support the idea that the area was fertilized with a product originated in a region of the Earth where the consequences of the global fallout due to nuclear weapons tests and/or the Chernobyl nuclear plant accident were important.