He said: 'Unfortunately the sport is not drug-free and I don't even think the race we just ran was drug-free.'
The 22-year-old sprinter from the University of Houston added: 'It takes a legitimate 10.2 sprinter maybe three years to get to 9.9. It takes a sprinter on drugs a month, maybe three months. But I'm not going to accuse anyone.'
Effiong said: 'We've all been drug- tested, so I think it was a pretty clean race.' The 21-year-old Nigerian will be a strong medal contender at the World Championships in Stuttgart this August.
The swimmer, Fraser Walker, won Britain's second gold in the men's 200m individual medley in 2min 04.48sec. Also in the pool, the British women's 800m freestyle relay team won silver behind Canada in a time of 8:26.67 after the US were disqualified for jumping the starting blocks.
Britain's football team lost 4-1 in the semi-finals against the Czech Republic. They play Germany in the bronze medal match tomorrow.
In the men's tennis final, Britain's Jeff Hunter lost in a four-hour match to Han Cheol Shin, of the Republic of Korea, 3-6, 6-3, 6-4, 3-6, 3-6.Reuse content