Loaded language is subtle, but evokes an emotional response in the reader. Loaded language is a powerful way to persuade the reader for or against a particular action.
Let's look at the given examples.
Clean-water regulations prevent businesses from dumping waste.
-- Here, the idea of "dumping" is certainly loaded. The writer could have used the term "disposing of waste," but instead chose to use the term "dumping." This word makes the reader think of trash, garbage, and filth.
The clean-water regulations are burdensome on businesses.
-- This sentence is persuasive but the term "burdensome" does not evoke an emotional response in the reader. While a burden is not positive, a burden on businesses is does not provoke feelings in the reader. Therefore, this sentence does not contain loaded language.
Regulations have resulted in cleaner rivers and lakes.
-- As it is written, this sentence does not provoke an emotional response in the reader. As such, it does not contain loaded language.
Businesses should not be prevented from disposing of waste however they see fit.
-- This sentence does not contain loaded language as it uses the neutral term "disposing of" instead of something that evokes an emotional response.
Therefore, the sentence that contains loaded language is the first example given: Clean-water regulations prevent businesses from DUMPING waste.