Which substances are typically not naturally found in surface waters?

Microplastics are typically not naturally found in surface waters because they are synthetic materials derived from human activities. They result from the breakdown of larger plastic debris or are intentionally manufactured for use in products such as cosmetics and industrial applications. Unlike suspended solids, nutrients, and salts, which are naturally occurring components in ecosystems and can originate from natural processes like erosion, biological activity, and weathering of rocks, microplastics are a pollutant created by modern society. Their presence in water bodies has been a growing concern due to their potential harmful effects on aquatic life and human health, highlighting the impacts of pollution as a result of human activities.