It is possible that this green powder stuff might be a mold. Molds are fungus which grow through spores. These spores are present in the environment and can grow to molds if find their favorable environment. Moist area is their most favorable environment. You should remove all this green powdery stuff by wearing gloves and mask. Make proper arrangements for ventilation. Repair water pipes leakage. You can also use kitchen cabinet cleaner which is available in the market.
