A Fourth of July weekend family barbecue in Valley Stream ended Friday night after guests were exposed to what police say was an unknown chemical substance, sending 10 people to the hospital.

Homeowner Keematie Rajroop said the gathering took a frightening turn when family members noticed a strong odor.

"We started smelling this strong scent. Our eyes started burning. Your throat was burning," Rajroop said.

According to Rajroop, the smell resembled vinegar. As family members tried to determine where it was coming from, one relative went to the back of the yard.

"My cousin-in-law went to the back of the yard to see, because it was coming from behind us. They saw the mist," she said.

Nassau County police allege the mist came from an unknown chemical substance that was sprayed by a neighboring resident, identified as 46-year-old Nicholas Stolz.

Rajroop said she called 911 after family members began experiencing difficulty breathing.

Ten people were taken to the hospital, including three children. Rajroop said everyone has since been released, but some relatives continue to experience lingering health issues.

"When we dropped them off at the airport, she was throwing up there as well. I have another cousin who went to the hospital. She was the last one to come out last night. She's still having problems internally, and we don't know the after-effects of what he did," Rajroop said.

Prosecutors said several partygoers suffered burning sensations and difficulty breathing.

Stolz's attorney said her client was simply spraying his grass.

The incident left neighbors shocked.

"I've lived here the past five years. I've never heard of this. People are friendly. But this is not good," said neighbor Mahesh Hadap.

Stolz was arraigned Saturday morning on 11 counts of assault and endangering the welfare of a child. He pleaded not guilty, was released and is scheduled to return to court on Wednesday, July 22.