I'm from the other side of Columbiana County, about 20 miles from EP. I have not read anything official or unofficial about livestock or even wild animals dying at abnormal rates, besides the chickens and pets mentioned in the Newsweek article listed just above, as well as fish in streams that flow through the evacuation zone. We have not noticed anything out of the ordinary here - no odors, no dead fish or livestock, and we dairy farm, so we have hundreds of cows. My inlaws are well-connected with dairy farmers around the county, and they would certainly hear about abnormal loss of livestock. There are people claiming online that they suddenly are not seeing birds/small wildlife like they did before (this is like 15 miles away from the derailment site), but there's no way to prove that.
People north of EP as far as Boardman reported strong chemical odors on Tuesday, the day following the controlled release, but I was there for a doctor's appointment on Wednesday and couldn't smell anything. The EPA has stated from the very beginning that they have never detected dangerous levels of chemical in their air monitoring, but of course, many people don't believe them.
All of this is MOO as a semi-local resident, but especially this: this area has been primed for conspiracy and distrust of authority over the last few years. It's to the point where I don't even know what information or evidence they would have to be presented, in order to trust what someone is telling them, and that's understandable to a point. There have also been online content creators - environmentalists, etc - that have jumped on this bandwagon. I think this is an incredible tragedy and only time will tell its effect on the environment, but everyone should be cautious to believe what they read, from all sides.