"CHARLESTON, W.Va. -- Obama administration officials on Friday proposed to update the federal government's 42-year-old exposure limits for silica dust, a move the Labor Department said would prevent 700 deaths and 1,600 new cases of silicosis every year. The proposal would provide new protections for 2.2 million American workers, cutting in half the legal limit for dust exposure on the job."

"California public health officials suggest limiting hexavalent chromium in drinking water to 10 parts per billion. Environmentalists say that's not nearly strict enough."

"The World Health Organization says that at least 135 people in China have been sickened by the H7N9 flu strain, and 44 have died. Most likely, these victims got the virus from chickens sold in live poultry markets. But where did the chickens get it? From ducks, who got it from wild migratory birds, scientists now say."

"For nearly a year, disease detectives around the world have been trying to track down the source of a mysterious new virus in the Middle East that has infected 96 people and killed 47 since September."

"Anti-government activists in Syria are accusing President Bashar al-Assad's forces of deploying a chemical weapons attack on the suburbs of the capital, Damascus. The government denied the attack, but the allegations have prompted the United Nations to call an emergency meeting. Melissa Block talks to Washington Post reporter Loveday Morris for more."

"U.S. drugmaker Merck & Co said on Friday it is suspending sales of its Zilmax animal feed additive in the United States and Canada following concerns about animals showing signs of distress after use of the product, which is given to cattle to increase their weight before slaughter."

"Officials raise alert as 'zombie' birds fall to earth amid fears city may be in grip of avian ailment Newcastle disease."

"The Centers for Disease Control and Prevention says 300,000 Americans are getting Lyme disease every year, and the toll is growing."

"New research finds that copper in amounts readily found in our drinking water, the foods we eat and the vitamin supplements we take likely plays a key role in initiating and fueling the abnormal protein build-up and brain inflammation that are hallmarks of Alzheimer's disease."

"While the mineral is important to healthy nerve conduction, hormone secretion and the growth of bones and connective tissue, a team of researchers from the University of Rochester Medical Center suggested that too much of it may be a bad thing, and they set about to explore copper's dark side.