What changes to the environment can affect the activity of enzymes

A variety/change in temperature and pH are the things that affect the activity rate of enzymes. Since enzymes only function at the certain pH and temperature level that they are most comfortable/used to, if that changes, then their activity rate will decrease.

an increase in temperature can increase enzyme activity (but not too high) and a cooler temperature decreases activity, an effect on Ph and this is not so much environment but how many enzymes there are in total