{"id":18035,"date":"2022-09-26T14:45:52","date_gmt":"2022-09-26T12:45:52","guid":{"rendered":"https:\/\/serveiseducatius.xtec.cat\/altemporda\/?p=18035"},"modified":"2022-09-26T14:47:12","modified_gmt":"2022-09-26T12:47:12","slug":"la-degradacio-del-plastic-a-locea-contribueix-a-la-seva-acidificacio","status":"publish","type":"post","link":"https:\/\/serveiseducatius.xtec.cat\/altemporda\/xarxa-escoles-cap-de-creus\/la-degradacio-del-plastic-a-locea-contribueix-a-la-seva-acidificacio\/","title":{"rendered":"La degradaci\u00f3 del pl\u00e0stic a l’oce\u00e0 contribueix a la seva acidificaci\u00f3"},"content":{"rendered":"

\"\"<\/a>Un nou estudi liderat per l’Institut de Ci\u00e8ncies del Mar<\/a>\u00a0(ICM-CSIC) de Barcelona ha revelat que la degradaci\u00f3 del pl\u00e0stic per efecte de la llum solar contribueix a l’acidificaci\u00f3 de l’aigua de mar. Aix\u00f2 \u00e9s degut a l’alliberament de compostos de carboni org\u00e0nic dissolt provinents tant del mateix pl\u00e0stic com dels seus additius, i a la producci\u00f3 de CO\u2082.<\/p>\n

“Gr\u00e0cies a aquest estudi hem pogut comprovar que en zones de la superf\u00edcie de l’oce\u00e0 molt contaminades per pl\u00e0stic, la seva degradaci\u00f3 podria donar lloc a una baixada de fins a 0,5 unitats del pH, cosa que \u00e9s comparable a la baixada de pH estimada en els pitjors escenaris d’emissions antropog\u00e8niques per a finals del segle XXI”, apunta <\/span>Cristina Romera-Castillo<\/strong>, investigadora de l’ICM-CSIC i primera autora de l’estudi, que s’ha publicat aquesta setmana a la revista\u00a0<\/span>Science of the Total Environment<\/a><\/em>.<\/span><\/p>\n

L’acidificaci\u00f3 i la contaminaci\u00f3 per pl\u00e0stic s\u00f3n dos dels grans problemes que afronta l’oce\u00e0 actualment. En aquest sentit, des de la revoluci\u00f3 industrial, l’augment de l’acidesa dels mars i els oceans est\u00e0 provocant que a alguns organismes calcificadors, com \u00e9s el cas dels coralls, els sigui m\u00e9s dif\u00edcil mantenir els seus esquelets. D\u2019altra banda, se sap que cada any arriben al mar uns 13 milions de tones de pl\u00e0stic, i s’estima que unes 250.000 tones m\u00e9s estan flotant per tot l’oce\u00e0.<\/p>\n

El proc\u00e9s d’acidificaci\u00f3<\/h3>\n

La llum ultraviolada procedent del sol \u00e9s el principal factor de degradaci\u00f3 i envelliment del pl\u00e0stic. Aquesta degradaci\u00f3 dona lloc a fractures que fan que el pl\u00e0stic es trenqui en trossos m\u00e9s petits, alguns de menys de 5 mil\u00b7l\u00edmetres, m\u00e9s coneguts com a micropl\u00e0stics.<\/p>\n

Com que est\u00e0 exposat a la llum solar i a l’erosi\u00f3, el pl\u00e0stic es troba “envellit\u201d, i el seu grau de degradaci\u00f3 dep\u00e8n del temps que porti exposat a aquestes condicions. Aquesta exposici\u00f3 dona lloc a un alliberament m\u00e9s gran de compostos qu\u00edmics a l’aigua i provoca una baixada del seu pH.<\/p>\n

Els compostos qu\u00edmics que el pl\u00e0stic allibera a l’aigua de mar durant la seva degradaci\u00f3 poden ser components del mateix pl\u00e0stic o b\u00e9 additius que se li afegeixen per donar-li color o\u00a0atorgar-li resist\u00e8ncia. Alguns d’aquests compostos s\u00f3n \u00e0cids org\u00e0nics, la qual cosa explica que contribueixin a la baixada del pH.<\/p>\n

Tanmateix, durant la degradaci\u00f3 del pl\u00e0stic tamb\u00e9 es produeix CO\u2082, que pot ser em\u00e8s directament per aquest, o b\u00e9 ser un producte de les reaccions que la llum solar desencadena en els compostos org\u00e0nics alliberats pel pl\u00e0stic. Alhora, aquest CO\u2082 alliberat interv\u00e9 en una s\u00e8rie de reaccions que tamb\u00e9 provoquen una baixada de pH de l’aigua.<\/p>\n

Difer\u00e8ncies entre el pl\u00e0stic nou i el vell<\/h3>\n

Per a l’elaboraci\u00f3 del treball, l’equip investigador va exposar diferents tipus de pl\u00e0stic (nou i envellit) a una temperatura i radiaci\u00f3 solar constants. Despr\u00e9s va analitzar el pH de l’aigua i la quantitat de carboni org\u00e0nic que alliberaven els micropl\u00e0stics a conseq\u00fc\u00e8ncia de la degradaci\u00f3.<\/p>\n

Amb nom\u00e9s sis dies d\u2019exposici\u00f3 a la llum solar, una barreja de pl\u00e0stics envellits recollida a les platges alliberava una gran quantitat de compostos de carboni org\u00e0nic dissolt i es va observar una disminuci\u00f3 significativa del pH de l’aigua. En els experiments amb pl\u00e0stic nou, en canvi, es va fer servir poliespan, polietil\u00e8 de baixa densitat (LDPE) -amb qu\u00e8 es fabriquen bosses i altres envasos-, i pl\u00e0stic biodegradable. D’aquests, nom\u00e9s el poliespan (poliestir\u00e8 expandit) va produir una baixada substancial del pH, ja que amb els altres no es van veure difer\u00e8ncies significatives.<\/p>\n

\n

“Aquests resultats posen de relleu que el pl\u00e0stic envellit afecta molt m\u00e9s que el nou a l’acidificaci\u00f3, la qual cosa \u00e9s molt preocupant, car la majoria del pl\u00e0stic que es troba al mar, sigui del tipus que sigui, est\u00e0 degradat”, conclou Romera-Castillo<\/p>\n<\/blockquote>\n

M\u00e9s info<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

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