Blueridgeoutdoors has a brief summary of what is known at present about environmental implications of the Haiti earthquake. As is usually the case with catastrophes like this, water and sanitation issues are paramount.
Fortunately, there have been few reports of ruptured tanks of fuel and the like, but that could change. One big problem is the debris from the earthquake, and where to put it.
Haiti’s population is currently increasing at about 1.84 percent per year, per the CIA World Factbook. With about 9 million people there now, this means that the population will reach about 12 million in 10 years, adding to the challenges there if population continues to rise at the current rate. (However, population growth is declining in Haiti; in 2008 the growth rate was 2.5%.)