A groundwater report can list dozens of pollutants under a landfill and still leave open which one deserves the first dollar of cleanup money. A new review argues that the answer often lies in toxicity and exposure, and that the size of a reading is a weaker guide.
The critical review examines how leachate moves from landfills into groundwater and how researchers estimate the health effects. Its authors, M. Bamini and R. K. Somashekar of Bangalore University, drew on more than 100 studies, focused on tropical urban aquifers but including temperate and engineered sites.
The Biggest Number Is Not Always the Biggest Hazard
Leachate is the liquid that drains through waste, and it can carry a mix of metals and organic chemicals. One study the review cites, covering 12 operating landfills in China's Guangxi Province, found that arsenic carried a calculated cancer risk roughly 2.3 times that of cadmium even though arsenic showed up at lower concentrations. Zinc produced the highest non-cancer hazard score of any pollutant measured. Those figures come from risk models and do not record actual illness.
A ranking built on concentrations, the authors argue, can put the wrong contaminant at the top of the list. For environmental, health and safety (EHS) teams and the finance staff who approve their budgets, a remediation proposal backed only by a table of exceedances leaves out toxicity and who might be exposed. U.S. Superfund practice already pairs the two, combining toxicity and exposure in the baseline risk assessment the Environmental Protection Agency (EPA) prescribes. Any applicable cleanup standard still has to be met however the rankings fall.
Pathways Decide What a Project Actually Fixes
Leachate also takes indirect routes. The review describes leachate seeping directly into aquifers and also moving through nearby ponds, lakes and drainage channels, which can turn a pond into a second source. In fractured rock, groundwater follows discrete cracks more than the pore spaces in the rock, so pollution can turn up where a simple model would not predict.
Capping a leaking cell, treating a plume that has already spread and protecting a well field are different projects with different payoffs. A proposal that names the pathway it cuts off and the people or water supply it protects is easier to weigh against alternatives. The same discipline applies to remediation of per- and polyfluoroalkyl substances (PFAS), where treatment and liability vary widely by site.
Ranking Tools Still Depend on Local Data
Researchers have built scoring systems that weigh persistence, migration, bioaccumulation and toxicity to decide which contaminants to chase first. The review notes that the results shift substantially depending on how those factors are weighted. It found no formally weighted prioritization study for tropical open dumps or municipal landfills.
Weather adds another variable. Heavy rain can flush contaminants into groundwater, while dry periods can concentrate them, and which effect wins depends on local geology, landfill age and rainfall. A single sampling round may miss the pattern entirely.
The authors call their work a structured narrative synthesis. It does not pool results or score the underlying studies for bias, so it offers a way to frame an investigation but no rankings that carry over from one site to another. Companies already treating water as a growing compliance exposure can bring that framing to the next remediation budget. The questions are familiar from corporate water management, namely which exposure each project reduces and how sampling will show it worked.
