The search came after green pellets, which initial tests indicated may be rat poison, were found at a Chermside playground in Brisbane's north.
Queensland's police chief, (mr) Paul Wilson, says detectives are still trying to identify the culprit behind the poison scare.
“Making nuisance and threats and threatening calls- those people can face substantial jail terms, placing poisonous items around- depending on the circumstances and depending on what charges will be laid- it would be remiss of me at this stage to indicate that. It's not quite clear, but as the investigation unfolds, that will become more clear and we will be in a better position,” Mr Wilson said.