while at the same time they have introduced some 100,000 dangerous chemical pollutants, having

while at the same time introducing some 100,000 dangerous chemical pollutants that have

while they have introduced some 100,000 dangerous chemical pollutants at the same time, and have

but introducing some 100,000 dangerous chemical pollutants at the same time that have

but at the same time introduce some 100,000 dangerous chemical pollutants, having