It is possible to dispose of these in the trash if you take suitable safety precautions.
Follow these steps:
See image below.
The plastic barrel of the syringe is recyclable polypropelene
If you have a large quantity of such syringes, you can separate all the barrels (the clear tube without plunger) from the rest of the syringe, rinse the barrels out, stock them up and pass them to plastify.sg. The rest of the needle should be disposed of safely per info above.
Syringes are considered biohazardous waste. Where possible, they should be disposed of with a medical establishment.
However if you take the necessary precautions, they can be disposed of safely in the trash.
