Liquid detergent can negatively affect the environment despite there being an easy fix. 

Due to common detergent being liquid, it has to come in a container that is waterproof, at least on the inside. This generally means that plastic is involved. This plastic is usually single use due to there being limited options for refilling detergent bottles, which means these single use plastic bottles typically end up in landfills. 

So what can you do?

Powder detergent. Powder detergent includes all the things that liquid detergent does, except the liquid. But since you are using this powder in a washing machine anyways, the liquid will be added while it is washing. It also typically comes in something that is not plastic, such as cardboard or paper. Thus you are saving money (powder detergent lasts longer and you aren’t spending money on the water that is in liquid detergent), saving the planet (less plastic waste), and it is just as easy to use. Therefore powder detergent is an easy solution to a bigger problem.

Try to do everything you can to help the environment, starting with this just easy example.