What are Herbicide tolerant crops in ecological

Herbicide tolerant crops (HTC)  Ecological 

a)  Increased use of the herbicides that plant is  tolerant to (describes ecological impact eg toxic residues in soil, run-off into waterways).

b)  There may also be a decrease in use of other herbicides (benefit to environment eg more diversity of plants).

c)  Weed resistance may lead to increase in use of other more toxic herbicides (describes ecological impact).

d) HTC plants could become weeds in subsequent crops as they become more difficult to eradicate. 

e)  less competition for the crop plant as the farmer can spray herbicide at anytime over crop.