The Hindu Business Line

How cli­mate change is rais­ing mer­cury lev­els in fish

Strin­gent reg­u­la­tions are needed to pro­tect hu­mans from ex­po­sure to this toxin, say re­searchers

- M SOMASEKHAR

Cli­mate change and over-fish­ing that is lead­ing to a shift in di­etary pat­terns are push­ing up the amount of toxic mer­cury in cer­tain fish pop­u­la­tion.

This is the find­ing of a study by an in­ter­na­tional con­sor­tia of the In­dian In­sti­tute of Tech­nol­ogy-Hy­der­abad (IIT-H), Har­vard Univer­sity, and Fish­eries and Oceans, Canada.

The team used modelling stud­ies and data of three decades from the Gulf of Maine in the At­lantic Ocean to ac­cess the im­pact of cli­mate change and other fac­tors on mer­cury ac­cu­mu­la­tion in fish. The work was pub­lished in the Au­gust is­sue of Nature.

The re­searchers showed that “As a re­sult of a change in the diet due to over­fish­ing, there was an in­crease in methyl mer­cury con­cen­tra­tion in At­lantic cod fish while there was a de­crease in the case of Spiny dog­fish dur­ing the past three decades.”

Ac­cord­ing to the model, a com­bi­na­tion of three fac­tors — 20 per cent re­duc­tion in methyl mer­cury con­cen­tra­tion in sea­wa­ter, one de­gree Cel­sius in­crease in ocean tem­per­a­ture and changes in diet — can ei­ther in­crease or de­crease the amount of methyl mer­cury present in fish.

Mi­na­mata Con­ven­tion

The find­ing is im­por­tant in view of the fact that global ef­forts to re­duce mer­cury lev­els in fish and other ma­rine an­i­mals through var­i­ous en­vi­ron­men­tal reg­u­la­tions have led to a drop in the over­all level of mer­cury pol­lu­tion.

The Mi­na­mata Con­ven­tion of Mer­cury that was en­forced in 2017 in­cludes a ban on new mer­cury mines, phase-out of ex­ist­ing ones and strict con­trol mea­sures on at­mo­spheric emis­sion.

The re­searchers, who fo­cussed on th­ese mea­sures, ob­served that the amounts of mer­cury found in fish have been different in different species — some have less than be­fore, while oth­ers have alarm­ingly more.

The con­sor­tia con­sisted of Asif Qureshi, Civil En­gi­neer­ing, IIT-H; and co-au­thored by Amina Schartup, Colin Thack­ray, Clifton Das­sun­cao, Kyle Gillespie, Alex Hanke and Elsie Sun­der­land.

Qureshi ex­plained: “There are three fac­tors that af­fect mer­cury ac­cu­mu­la­tion in fish — over­fish­ing, which leads to di­etary changes among ma­rine an­i­mals; vari­a­tions in the sea­wa­ter tem­per­a­ture, which leads to changes in fish me­tab­o­lism that em­pha­sises sur­vival rather than growth; and changes in the amount of mer­cury found in sea­wa­ter as a re­sult of pol­lu­tion.”

Con­ta­gion pos­si­bil­ity

Although this study was car­ried out in the At­lantic Ocean, mer­cury lev­els in fish in other seas and oceans are likely to have a sim­i­lar re­la­tion­ship with the sea tem­per­a­ture, fish­ing prac­tices and mer­cury pol­lu­tion lev­els, the re­searchers said.

Reg­u­la­tory ef­forts must not only con­trol the re­lease of mer­cury into the at­mos­phere, but also sig­nif­i­cantly re­duce green­house gas emis­sions that lead to sea­wa­ter warm­ing. Only by tack­ling both mer­cury emis­sions and global warm­ing can the lev­els of tox­ins be re­duced.

The re­searchers warn that hu­man ex­po­sure to the tox­ins through fish con­sump­tion is bound to in­crease as a re­sult of cli­mate change. There­fore, stronger reg­u­la­tions to pro­tect the ecosys­tem and hu­man health are needed

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