Mutations could be harmful if they change the codes for protein synthesis in such a way that a particular protein will not be able to conduct its routine function and will cause ailment. However not all mutations are harmful, there are very few number of mutations that actually can change the codes for a better functioning protein.
When a mutation alters a protein that plays a critical role in the body, it can disrupt normal development or cause a medical condition. A condition caused by mutations in one or more genes is called a genetic disorder. In some cases, gene mutations are so severe that they prevent an embryo from surviving until birth.
One example would be the chemicals they use in the soil to make the plants grow faster and another example would be chemicals they use to kill pest so they wont eat the crops or you could say bioengineering has enhanced the crops
