There are times when insecticide residues exceed the Maximum Residue Limits (MRL) in pechay available in the market. This was reported by Dr.Susan May F. Calumpang and Dr. Gil Magsino of the Crop Protection Cluster of the College of Agriculture at UP Los Baños.
In their experiments, they tested the commonly-used insecticide in pechay. They say that this is really a concern for consumers as it could impair their health. To be safe, Dr. Calumpang stresses that pechay leaves be soaked in a 10 percent vinegar solution before cooking. This is done by mixing 10 tablespoons of vinegar in a liter of water into which pechay is soaked for 2 to 5 minutes. This could reduce the residue by up to 80 percent.