A European Union court ruling on an Eastern European waste dispute highlighted a possible gap in EU legislation, which might lead to the disposal of chemical substances that could be recycled.

The Luxembourg-based Court of Justice on March 14 dismissed a case brought by the European Commission, the EU’s executive arm, which had alleged the Czech Republic infringed EU law by refusing to take back a shipment of hazardous waste.

Under EU law on waste shipments, hazardous waste can...