Image copyright Pennsylvania police Image caption The student is a chemistry major and said he purchased the thallium to use on himself

A Chinese chemistry student at a US university tried to poison his African American roommate over a period of several months, prosecutors allege.

Yukai Yang was charged with attempted homicide and arrested on Thursday.

Prosecutors say he laced the food and drink of Juwan Royal with thallium. Mr Royal still suffers symptoms.

Mr Yang admits buying chemicals but says they were intended for his own use. He is also charged with writing racist graffiti in their dorm room.

The alleged poisoning took place over several months in the spring of 2018 when Mr Royal, a fellow senior at Lehigh University in Pennsylvania, sought medical help several times for feeling dizzy, passing out, throwing up and feeling shaky, prosecutors say.

Mr Yang admitted to having purchased thallium and other chemicals on the internet but said he got them "with the intent for him to harm himself if he did poorly on future exams", District Attorney (DA) John Morganelli told reporters.

According to Mr Morganelli, "Mr Royal experienced extreme pain in his lower extremities as well as severe burning and numbness which resulted in intensive medical treatment."

The DA said the poisoning went on over a long time and the victim continued to suffer from the symptoms to this day.

Image copyright facebook/lehighu Image caption Both students had been living together at Lehigh University for years

Odourless and colourless thallium is a chemical element that can be lethal for humans. It was also used in rat poison in the past and is still part of electronics manufacturing.

Mr Yang was already facing charges over ethnic intimidation linked to racist graffiti written in their dorm room.

Police said they traced the handwriting to the Chinese student.

The two had reportedly shared lodging for several years during their studies and Mr Royal thought they were friends until presented with the lab results.