The Dal Lake in Srinagar is accumulating toxic heavy metals at rates that can raise the concentration of arsenic 239-fold, lead 76-fold, and mercury 100-fold within 35 years, a study has suggested.

People exposed to heavy concentrations of these metals — for instance, by eating contaminated fish — can suffer serious ailments ranging from neurological damage to higher risks of certain cancers. The researchers said the “current concentrations are concerning but not alarming” yet.

The study by scientists at the University of Kashmir is among the first to forecast the future concentrations of these toxic metals in the freshwater lake, although multiple earlier studies had flagged pollution threats to the lake’s ecosystem.

The Dal Lake, spanning 24sqkm and fed by five streams, is a focal point for tourism, offering boat rides, houseboat stays, supporting local livelihoods and fisheries.

Environmental scientists have, however, long been concerned that poorly treated sewage, agricultural chemicals runoff, and emissions laced with heavy metals deposited into the lake might ravage its chemistry.

“Most previous studies involved one-time snapshots of pollution in the lake,” said Shahnawaz Hassan, a research scholar at the university’s environmental science department.

“We’ve tried to understand how metal concentrations have changed over time and might increase in the future.”

Hassan and his colleagues sampled sediments from the bottom of the lake, using pipe-like equipment to extract long cylindrical chunks of them. As sediments accumulate over hundreds to thousands of years, the top layer represents the most recent sediments while the bottom layer represents the oldest.

The researchers found the highest concentrations of heavy metals in the top layer, with the figures decreasing in the lower sections. The lowest concentration was in the bottom layer, dated to be 3,700 years old, a pattern consistent with more and more metals being deposited over the years.

The topmost layer had 0.92 micrograms of arsenic per gram of sediment, 64 micrograms per gram lead, and 0.006 micrograms per gram mercury. The study’s findings have just been published in the journal Environmental Chemistry and Ecotoxicology.

The researchers have used a time trend analysis to forecast that if the current heavy metal accumulation rates in the lake remain unchanged, the concentration of arsenic will increase 239-fold, lead 76-fold, and mercury 100-fold within the next 35 years.

“The current concentrations are concerning but not alarming. In 35 years, they will be at alarming levels,” Hassan said.

“We’re hoping our results will prompt more research to identify specific potential sources of the heavy metals coming into the lake and take steps to check this flow.”

Lead and mercury can accumulate in the tissues of fish, impairing their reproductive success. Studies in European and North American lakes have documented significant declines in fish populations because of mercury-induced reproductive failure.

Heavy metals can enter the human food chain through a process known as bio-magnification, in which the concentrations of metals increase as they move up the food web. People who eat contaminated fish can face the health risks of heavy metal exposure.

Exposure to high levels of arsenic, lead, or mercury can cause neurological damage, organ failure, development disorders, and an increased risk of certain cancers, among other health hazards.