Final answer:
The environmental issue in question is nuclear waste leading to health hazards such as cancer and birth defects, prevalent in countries like the United States. International cooperation is required to address environmental problems that exceed national boundaries.
Step-by-step explanation:
The environmental issue of nuclear waste, along with associated high rates of cancer and birth defects, can be found in multiple countries, but a prominent example is the United States. This is due to the historical and ongoing operations involving nuclear power and weapons development.
Countries across the globe face the international externality of environmental challenges that transcend national borders, such as global warming and biodiversity loss, necessitating cooperative international agreements. Environmental challenges related to nuclear energy include uranium mining, production of reactor fuel, and the management of radioactive waste. These materials pose a health hazard for thousands of years due to long radioactive half-lives.