Was the chemi waste bottle previously used for radioactive waste? Are you probing the filter first with 32P and then stripping and rehybridising with ECL ?

What level of contamination are you measuring and have you checked all of the apparatus and reagents for 32P

Does the chemi waste in the waste bottle show 32P contamination ?

Based on your description, it’s highly unlikely that maleic acid is the source of the radiation signal you're detecting at the waste bottle, as maleic acid does not possess any radioactive properties nor does it absorb or emit radiation. In your chemiluminescent southern blot trial, where you're replacing P32 with a non-radioactive detection method, such as DIG-based chemiluminescence, the signal you're seeing is most likely due to residual chemiluminescent substrate (like luminol or its derivatives) and HRP enzyme activity in the waste. These components can continue to emit light for some time after disposal, and sensitive detectors or radiation monitors, especially if not specifically designed to distinguish between ionizing radiation and low-level light emission, can falsely interpret this as radiation. If you're using a Geiger counter calibrated for beta emissions and it’s giving a signal at the bottle tip, double-check that no surfaces or gloves were contaminated with previous P32 work, though you mentioned you're sure there's no such contamination. To confirm the signal's source, try isolating the chemiluminescent waste from your detector or switching to a detector that specifically distinguishes radiation from light emission. In short, maleic acid is not the issue, t's more likely a false signal caused by lingering chemiluminescent activity or detector sensitivity.