IETU has got wide experience in international co-operation due to its participation in projects realised for many foreign organisations, in that: World Health Organisation (WHO), U.S. Environmental Protection Agency (U.S. EPA) and the U.S. Department of Energy (DOE).

Under the intergovernmental agreement IETU staff has been participating in Working Groups and Task Forces of the ECE/UNO, Convention on Long-Range Transboundary Air Pollution (LRTAP).

Under the bilateral governmental agreement between Poland and Norway IETU has been co-operating with the Norwegian Institute of Water Research (NIVA) on acidification of lakes in Tatra Mountains.

IETU has got three direct multi-year agreements on research and scientific co-operation with foreign institutions (renewed) and two arrangements on multi-year co-operation:

• Agreement for Technical Exchange and Co-operation between the U.S. Department of Energy (U.S. DOE) concerning joint projects in the field of environmental revitalisation and hazardous waste problems, concluded in 1995 and extended in 2000 for the next 5 years

• Agreement for Co-operation with Florida State University (FSU) signed in 1996, concerning exchange of scientific information, organisation of scientific conferences, education and joint research projects
• Agreement with the Norwegian Institute of Air Research (NILU) signed in 1996 and extended in 1998, concerning exchange of scientific information, organisation of scientific conferences and workshops, joint research projects, exchange of experts
• Memorandum of Understanding with the Institute of Mineralogy, Geochemistry and Crystallography of Rare Elements (IMGRE) signed in 1998, regarding exchange of information on technologies for soil cleanup from persistent contaminants

Memorandum of Understanding with the Institute of Soil Treatment of the Russian Academy of Agricultural Sciences in St. Petersburg on undertaking joint efforts for the development of methods and techniques in the field of ecology and geochemistry, concluded in 1998.