Cadmium-Contaminated Durian: Soil and Fertilizer Are Also Part of the Equation

Why durians become contaminated with cadmium, the role soil pH plays, and how to choose suitable fertilizers to reduce heavy metal risks for export-oriented durian orchards.

Since 2023, numerous batches of Vietnamese durian exported to China — a market that accounts for more than 90% of the country's total durian export value — have been flagged or returned due to cadmium residues exceeding permitted limits. This is no longer an issue confined to a handful of shipments; it is becoming a shared risk for entire growing regions unless addressed at the root cause.

Where does cadmium come from

Cadmium is a heavy metal that occurs naturally, often found alongside certain phosphate and zinc ores. It can already be present in soil in areas near mining sites, enter through contaminated irrigation water, or come from certain fertilizers that contain cadmium as an accompanying impurity. Durian trees, compared with many other crops, tend to absorb heavy metals through their roots quite strongly, so even soil or irrigation water contaminated at a relatively low level can still allow the fruit to accumulate cadmium beyond the permitted threshold.

Why acidic soil makes cadmium more likely to enter the plant

In acidic soil, cadmium exists in a more mobile form, dissolving more easily in the soil solution and being more readily absorbed by plant roots. Conversely, when soil pH is raised closer to neutral, cadmium tends to be held more tightly in the soil in a less soluble form, limiting the amount the plant can take up. This is why many current technical recommendations view raising soil pH as one of the most effective measures for reducing cadmium risk in the fruit.

Choosing the right fertilizer is also part of the solution

Because of its alkaline nature, fused magnesium phosphate fertilizer helps raise soil pH over time, unlike certain acidic fertilizers that can make soil more acidic with long-term use, indirectly making cadmium in the soil more mobile. In addition, not all phosphate fertilizers carry the same heavy metal content straight from the source ore. Choosing products with controlled cadmium and arsenic levels right from the raw material stage — the same standard that Lao Cai fused magnesium phosphate fertilizer applies in order to qualify for export to Japan and South Korea for tea and citrus regions — is also a way to reduce the risk of introducing additional cadmium into the soil from the outset.

This is not the only solution

Raising soil pH and selecting fertilizers with controlled heavy metal content are only part of the overall picture. Farmers growing durian for export still need to test their soil and irrigation water sources before planting or expanding cultivation area, avoid overusing growth stimulants and unverified foliar fertilizers, and periodically send soil and fruit samples for analysis before each harvest season to proactively detect any abnormalities early.

The cadmium issue in durian will still require time and a combination of coordinated measures to bring fully under control. But starting with a correct understanding of the role soil and fertilizer play in that entire chain is a step every orchard can take proactively starting from the next crop cycle.