Soviet-era chemical agents; a pond full of sewage that children use as a play area; highly radioactive material — these are just a few of the environmental and health hazards found so far in Kabul, Afghanistan, by U.N. peacekeepers and a team of U.N. scientists that began an environmental assessment of the country last week. The situation outside of the capital city is no better. About half of the nation’s forests (which at their peak covered just 3 percent of the country) have been logged, leading to desertification. Water is in very short supply after a four-year drought, and what little remains is frequently contaminated; rates of water-borne diseases such as cholera and diarrhea are high. Still, despite war, poverty, drought, and desperation, Henrik Slotte, who heads the U.N. Environment Programme’s assessment unit, found room for optimism: “This is exactly the moment when you can turn the page and start over,” he said.