To many Koreans, judging from past actions, this fear is reasonable. Look at koguryo. And Gangdo. All, right, just go to this search I made at the Marmot's hole.
And why not? Norht Korea is said to have great natural resources that the locals were unable to recover and exploit. Plus, the population is less well-off than China's so any assistance would go a long way.
Here is why not. From the Dong-a:
North Korean organizations in charge of raising foreign currency are bringing in and burying industrial waste from China for money, a report released yesterday said.
One North Korean scientist said, “Our country in effect is turning into China’s industrial waste site,” adding, “Even tap water in Pyongyang has become so polluted that it is no longer potable.”
North Korea is reportedly taking in foreign industrial waste in secret in the form of its border trade with China.
Dong Yong-seung, head of the economics and security team at Samsung Economic Research Institute in Seoul, said, “Though no data is available that can tell us the exact situation, Chinese companies might believe that sending industrial waste to North Korea for burial is cheaper than disposing of it in China in compliance with Chinese environmental regulations.
North Korea is also not just bringing in waste just from China. Former North Korean defector Kim Heung-kwang, now head of a coalition of former North Korean intelligentsia in South Korea, said, “Companies that earn foreign currencies brought in waste vinyl from Germany and France for 300 U.S. dollars per ton in early 2000 and buried it in soil.”
I suspect that if China is sending toxic waste to North Korea, the Norks aren't carting it across the entire country, yet perhaps we need to even more closely monitor the water that crosses the DMZ.