Let's have a look at the last clause:
каждый житель планеты употребляет вместе с едой и питьем 5 граммов микропластика — целую кредитную карточку — в неделю
• The subject is каждый житель планеты with житель being the head of the noun phrase, in the Nominative case.
• The predicate is употребляет “consumes” which is a transitive verb. ‘Transitive’ means it can have a direct object, and in Russian a typical direct object is a noun phrase in the Accusative case and without any preposition, e.g. in Я тебя люблю the direct object is тебя and it is in the Accusative case and without any preposition.
• The direct object is 5 граммов микропластика with 5 (пять) being the head of the phrase, in the Accusative = Nominative case without any preposition. It is followed by a so-called пояснительная конструкция “explanatory construction”, a phrase explaining what precedes it. Typically, such constructions are singled out with commas, long dashes, or a colon, in your sentence the first long dash was chosen because the construction is introduced without any conjunctions, and there is the second long dash at the end of the construction since the sentence is not yet over, an adjunct of time follows (в неделю “every week”).
Since that explanatory construction just explains the direct object, mirrors it, paraphrases it in terms of a 5-gram piece of plastic everybody can imagine, it is also in the Accusative case without any preposition, just like the direct object itself.
The best way to get rid of the long dashes is to introduce that explanatory construction with a conjunction, for example, with то есть “that is”, in this case the construction will be framed with commas:
каждый житель планеты употребляет вместе с едой и питьем 5 граммов микропластика, то есть целую кредитную карточку, в неделю