The Trou­ble with Mi­croplas­tics

by Me­chas

Mi­croplas­tics, a term used for plas­tic par­ti­cles rang­ing from 1 μm to 5 mm in size, are pol­lu­tants present in soils, wa­ter, air, on and in plants, in the food we con­sume, and in our bod­ies. On plants, for ex­am­ple, mi­croplas­tics de­crease pro­duc­tiv­ity due to a 7 to 12 % re­duc­tion of pho­to­syn­the­sis. More wor­ri­some are re­ports of plas­tic par­ti­cles in sam­ples of hu­man kid­ney, liver, and, amaz­ingly, in the brain. In essence, mi­croplas­tics are ubiq­ui­tous, per­sis­tent, and, ap­par­ently, un­avoid­able. 

The scaled num­ber emis­sions (color shad­ing) and con­tri­bu­tion of the land emis­sions to the sim­u­lated val­ues over the ocean (col­ored X mark­ers). Source. Fron­tispiece: Mi­croplas­tics. Source

More re­cently, sci­en­tists came up with new cal­cu­la­tions of plas­tic par­ti­cles in the at­mos­phere. By com­pil­ing a global at­mos­pheric dataset of mi­croplas­tics and tak­ing into ac­count size ranges, they were able to fine-tune pre­vi­ous es­ti­mates. Mi­croplas­tics are emit­ted into the at­mos­phere at about 3x10¹⁷ par­ti­cles per yr, a value that, though large, is nonethe­less about two or­ders of mag­ni­tude lower than pre­vi­ously thought. And not sur­pris­ingly, most of these come from land sources rather than from the oceans. While these es­ti­mates may change as more data roll in, they re­veal the mag­ni­tude of mi­croplas­tic emis­sions, which mi­grate and con­t­a­m­i­nate re­gions far and wide. 

The di­ver­sity of mi­croplas­tics rep­re­sents an ad­di­tional chal­lenge. These par­ti­cles dif­fer in com­po­si­tion, shape, sur­face prop­er­ties, and size, all of which sig­nif­i­cantly in­flu­ence how they be­have within a par­tic­u­lar en­vi­ron­ment. Dif­fer­ent-sized par­ti­cles, for ex­am­ple, will vary in their ca­pac­ity to be car­ried across dis­tances and tra­verse bar­ri­ers, such as tis­sues in or­gan­isms. The unique prop­er­ties of a mi­croplas­tic par­ti­cle trans­late into dif­fer­ences in the re­lease of chem­i­cals and their ca­pac­ity to at­tract and trans­port biofilm-form­ing mi­crobes. In sum, the com­plex and het­ero­ge­neous na­ture of these par­ti­cles com­pli­cates gen­er­al­iza­tions of their down­stream ef­fects. 

Fi­nally, the ac­cu­racy of meth­ods used to de­tect and quan­tify mi­croplas­tics, es­pe­cially in hu­man tis­sues, has been ques­tioned. As these tech­niques im­prove, so will our abil­ity to as­sess their preva­lence and po­ten­tial health ef­fects. But there is no doubt that the ac­cu­mu­la­tion of mi­croplas­tic par­ti­cles, an un­fore­seen con­se­quence of hu­man in­no­v­a­tive spirit, will con­tinue to test our ca­pac­ity to adapt to a chang­ing planet.