Plastiek besoedel die omgewing; daarom skei en sorteer ons die afval.

Because plastiek is being used in a general sense, like English Plastic pollutes the environment. Afrikaans often leaves out the article when talking about a material or a thing in general.

• Plastiek besoedel die omgewing = plastic in general pollutes the environment.
• Die plastiek besoedel die omgewing would usually mean some specific plastic.

Die is the Afrikaans definite article, meaning the.

A useful thing to remember is that Afrikaans uses die for:

• singular nouns
• plural nouns
• all grammatical genders

So:

• die omgewing = the environment
• die afval = the waste

Afrikaans does not change the the way some other languages do.

Yes. Besoedel is a standard and very common word for pollute/contaminate, especially in environmental contexts.

Examples:

• Fabrieke besoedel die lug. = Factories pollute the air.
• Chemikalieë besoedel die water. = Chemicals pollute the water.

You may also see vervuil, which can mean dirty or pollute, but besoedel often sounds a bit more formal or precise in environmental language.

Daarom means therefore, for that reason, or that is why.

It connects the two ideas logically:

• plastic pollutes the environment
• therefore we separate and sort the waste

So daarom introduces the result or consequence of the first clause.

Because Afrikaans main clauses usually put the finite verb in the second position.

Compare:

• Ons skei en sorteer die afval.
• Daarom skei en sorteer ons die afval.

When daarom is moved to the front, it takes the first position. The verb then has to come next, so the subject ons moves after the verb phrase.

This is a very common Afrikaans pattern:

• Ons doen dit.
• Vandag doen ons dit.
• Daarom doen ons dit.

They are close in meaning, but not identical.

• skei = separate
• sorteer = sort into categories

In a recycling context, skei en sorteer suggests both:

1. separating waste from other things, and
2. putting it into the correct groups

So it sounds natural and slightly more complete than using only one verb.

Afval is usually treated as a mass noun or collective noun, much like English waste.

So even if it refers to many pieces of rubbish, Afrikaans often uses the singular form:

• die afval

This is normal. It does not mean there is only one item of waste.

Depending on context, Afrikaans can also use words like:

• vullis = rubbish/garbage
• rommel = junk/mess
• afvalstowwe = waste materials

Not directly in this sentence, because daarom gives a result, while want and omdat give a cause.

• daarom = therefore / that is why
• want = because / for
• omdat = because

So the original sentence means:

• Plastic pollutes the environment; therefore we separate and sort the waste.

If you want to use want or omdat, you have to reverse the logic:

• Ons skei en sorteer die afval, want plastiek besoedel die omgewing.
• Ons skei en sorteer die afval omdat plastiek die omgewing besoedel.

The semicolon links two complete clauses that are closely related in meaning.

Here, both parts could stand alone:

• Plastiek besoedel die omgewing.
• Daarom skei en sorteer ons die afval.

The semicolon shows a strong logical connection between them, and it is a bit more formal than using a full stop. In everyday writing, a full stop would also be fine.

A rough guide:

• Plastiek ≈ plas-TEEK
• besoedel ≈ buh-SOO-duhl
• omgewing ≈ om-khuh-veng or om-ghuh-veng
  The g is the throaty Afrikaans sound, not an English hard g.
• daarom ≈ DAA-rum
• skei ≈ a bit like skay
• sorteer ≈ sor-TEER
• afval ≈ AF-fahl

These are only approximate English-style guides, but they can help you get started.