أكياس النفايات قليلة. مع ذلك يجمع المتطوعون النفايات البلاستيكية.

This is an iḍāfa construction, the very common Arabic X of Y pattern.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can take الـ
• the whole phrase gets its definiteness from the second noun

So أكياس النفايات literally means bags of the waste, which is the natural Arabic way to say garbage bags.

Also, the singular of أكياس is كيس.

Because in Modern Standard Arabic, non-human plural nouns usually take feminine singular agreement.

So even though أكياس is plural, it is:

• non-human
• therefore often treated grammatically as feminine singular for adjectives and predicates

That is why you get قليلة rather than a masculine plural form.

The same thing happens later with النفايات البلاستيكية: النفايات is plural and non-human, so البلاستيكية is also feminine singular.

Because here قليلة is not an attributive adjective inside the noun phrase. It is the predicate of the whole sentence.

So the structure is:

• أكياس النفايات = the subject
• قليلة = the predicate, meaning are few

In other words, this is a nominal sentence: Garbage bags are few.

If you wanted the few garbage bags as one noun phrase, then you would say أكياس النفايات القليلة with الـ on the adjective.

مع ذلك is a set phrase meaning:

• nevertheless
• however
• even so
• despite that

Literally, it is something like with that, but in real usage it functions as a connector between two ideas.

So here it links:

• There are few garbage bags
• Nevertheless, the volunteers collect the plastic waste

Because in this sentence the verb comes before the subject:

• يجمع المتطوعون ...

In standard Arabic, when the order is verb + subject, the verb is often singular, even if the subject is plural.

So:

• يجمع المتطوعون = the volunteers collect
• but if the subject came first, you would normally say المتطوعون يجمعون

So both are possible, but the agreement changes with the word order.

Because المتطوعون is a sound masculine plural in the nominative case, and it is nominative because it is the subject of the verb.

Its singular is متطوع = volunteer.

The endings are typically:

• -ون in the nominative
• -ين in the accusative and genitive

So here:

• المتطوعون = correct, because it is the subject

Because البلاستيكية is an adjective directly modifying النفايات, and Arabic adjectives normally agree with the noun in definiteness.

Since the noun is definite:

• النفايات = the waste the adjective must also be definite:
• البلاستيكية = the plastic

So:

• النفايات البلاستيكية = the plastic waste

This is different from قليلة, which is a predicate, not a directly attached adjective.

This is the same non-human plural rule seen earlier.

النفايات is:

• plural
• non-human

So in standard Arabic, its adjective usually appears in the feminine singular:

• النفايات البلاستيكية

This may feel strange to an English speaker, but it is a very common Arabic pattern.

It can mean either, depending on context.

The Arabic imperfect tense can express:

• a habitual/general present: they collect
• an ongoing present: they are collecting

So يجمع المتطوعون النفايات البلاستيكية could mean:

• The volunteers collect the plastic waste or
• The volunteers are collecting the plastic waste

The surrounding context usually tells you which is intended.

Because Arabic usually does not write short vowel endings in normal text.

The first النفايات in أكياس النفايات is part of an iḍāfa, so it is genitive.

The second النفايات in يجمع المتطوعون النفايات البلاستيكية is the direct object, so it is accusative.

But with a feminine sound plural like نفايات, the accusative and genitive endings are both normally -اتِ, so even with full vowels they would be very similar.

So the word’s function changes, but the written form usually stays the same.