Heavy Metals in Matcha: What We Test for and What Our Results Show

Lead, arsenic, cadmium, mercury — and why testing at origin in Japan is the only meaningful checkpoint in the supply chain.

If you drink matcha regularly and you haven't thought about heavy metals yet, this article is worth your time. If you have, and you've been looking for a brand that will actually show you results rather than just claim to test, read on.

The conversation around heavy metals in matcha has grown significantly in 2025 and 2026. Independent consumer advocates and food safety researchers have been testing popular matcha brands and publishing their findings. Some of the results have been concerning. Brands marketing themselves on purity — with phrases like "quadruple toxin screened" — have tested positive for detectable levels of lead, cadmium, mercury, and arsenic.

At Maison Koko, we think this conversation is important and overdue. Transparency isn't a marketing strategy for us; it's the minimum standard we think every matcha brand should be held to. This article explains what heavy metals are, why they matter in matcha specifically, what Japan's food safety framework actually involves, and what our own test results show.

Why heavy metals in matcha are worth taking seriously

Tea plants are natural accumulators. They draw minerals from the soil as they grow — and where soils contain elevated levels of heavy metals, the plant absorbs them. This is not unique to tea. It is a characteristic of many plants, and it is why the origin and farming conditions of any agricultural product matter.

With matcha, the concern is more acute than with any other form of tea. When you drink a regular green tea, you brew the leaves and discard them. Most of the plant matter — and any contaminants within it — stays in the leaf you pour away. With matcha, you consume the entire ground leaf. Every part of the plant goes into your cup. This concentration effect is what makes testing so important.

This is also why grade matters. The younger, more carefully tended leaves used in ceremonial-grade matcha accumulate fewer contaminants over their shorter growing cycle than older, lower-grade leaves — one of several important differences between grades that most buyers don't know about.

The four metals most commonly tested for:

• Lead: A neurotoxin with no established safe level of exposure for human beings, particularly for children, pregnant women, and women of childbearing age. Lead in matcha originates from the soil and growing environment.
• Arsenic: A known carcinogen found naturally in some soils. Inorganic arsenic — the form most harmful to human health — is the primary concern in agricultural products.
• Cadmium: A carcinogen that accumulates in the kidneys over time and has been linked to bone density loss with chronic exposure.
• Mercury: A neurotoxin of particular concern for pregnant women and developing foetuses. There is no established safe level of mercury ingestion.

None of these metals are added to matcha. They occur naturally at varying levels depending on where and how the tea is grown. The question is not whether any trace amounts exist; it is whether those levels are within safe limits, and whether the brand you are buying from actually knows.

The concern with heavy metals is not a single cup; it is chronic daily exposure over time. For occasional drinkers, the risk calculus is different. For someone switching from coffee to matcha and drinking one or two cups every day, knowing your matcha comes from a tested, traceable source is a reasonable priority.

What the testing landscape looks like right now

Independent consumer testing in 2025 and 2026 has produced a wide spectrum of results across matcha brands, and the findings are instructive. The research points to one consistent conclusion: origin matters more than any marketing claim.

Geographic origin plays a critical role in heavy metal content. Tea grown in regions with industrial pollution, high naturally occurring mineral soil content, or less rigorous agricultural oversight consistently performs worse on testing than matcha from carefully managed Japanese farms. But even within Japan, results vary by region, farm, grade, and harvest timing.

What the testing landscape also reveals is a credibility problem. Brands that use strong purity language — "toxin screened," "lab verified," "pure" — without publishing or sharing actual results are asking consumers to take their word for it. In a market where independent testing has found detectable heavy metals in several well-known brands, that is no longer a sufficient position.

Why Japan's food safety framework is genuinely rigorous

Japan's food safety system is governed by the Food Sanitation Act, administered by the Ministry of Health, Labour and Welfare (MHLW). For agricultural products, the key regulatory instrument is the Positive List System, which establishes maximum residue limits for over 700 agricultural chemicals. Any substance not explicitly listed defaults to a strict 0.01 ppm limit — effectively a prohibition in practice.

This is not aspirational. For matcha producers in regions like Yame, Fukuoka or Shizuoka, compliance with these standards is the baseline, not a differentiating feature. The entire supply chain, from cultivation through processing, operates within this framework.

Testing happens in Japan, before export, before the product leaves the country. This means the regulatory checkpoint occurs at the strictest point in the supply chain, not after the product has moved through international logistics. 

What Maison Koko tests for — and what our results show

Our matcha range is batch-tested by accredited labs in Japan before it reaches you. The four heavy metals — lead, arsenic, cadmium, and mercury — are tested.

Below is an example of a batch test report from our range. All four metals returned not detected across all limits of detection.

Example batch test report issued by an accredited Food Analysis Office in Japan, June 27, 2025. Lead, Cadmium, Total Mercury, and Arsenic all returned Not Detected. Detection limits: Lead 0.3ppm, Cadmium 0.05ppm, Mercury 0.01ppm, Arsenic 0.2ppm. Method: Atomic absorption spectrometry.

Our results at a glance:

• Lead: Not Detected (detection limit: 0.3 ppm)
• Cadmium: Not Detected (detection limit: 0.05 ppm)
• Total Mercury: Not Detected (detection limit: 0.01 ppm)
• Arsenic: Not Detected (detection limit: 0.2 ppm)

While we do not publicly release full certificates of analysis — as those documents contain supplier information we are committed to protecting — selected testing summaries may be shared with customers upon request. Any shared documents will have supplier information redacted to protect the privacy and intellectual property of our farming and production partners. Contact us at hello@maisonkoko.com with any questions.

What to look for when buying matcha

Whether you buy from us or elsewhere, here is what every informed matcha buyer should consider:

Origin matters more than certification

Organic vs non-organic is one of the most common questions we receive, and the answer matters here: organic certification is valuable; it means the tea was grown without synthetic pesticides, but it does not guarantee low heavy metal levels. Heavy metals occur naturally in soil. A certified organic matcha can still have elevated metal levels if the soil is naturally high in those minerals. Look for specific origin details: region, prefecture, and ideally the type of farm.

First harvest leaves perform better

First harvest, shade-grown ceremonial matcha tends to perform better on heavy metals than later-harvest, lower-grade culinary matcha. Younger leaves have had less time to accumulate environmental contaminants, and high-quality cultivation involves better soil management overall.

Ask for testing evidence

Any reputable brand selling matcha for daily consumption should be able to tell you what they test for, when they test, and who conducts the testing. 

Be skeptical of absolute claims without evidence

Phrases like "100% toxin-free" or "quadruple toxin screened" without accompanying results are marketing language, not safety guarantees. Independent testing in 2025 and 2026 has shown that some brands using this language have still tested positive for detectable levels of heavy metals.

The most credible brands communicate specifically: what metals, what methodology, what standards, what results.

Consider how often you drink it

The concern with heavy metals is not a single cup; it is chronic daily exposure over time. If you drink matcha every day, knowing your source is tested and traceable is a reasonable priority.

Why this conversation is good for matcha

The growing scrutiny of matcha safety is not a threat to the category. It is exactly the corrective force a maturing premium market needs. Informed buyers, independent testing, and transparency expectations will over time distinguish the brands doing things properly from those that are not.

Frequently Asked Questions: Heavy Metals in Matcha

Does all matcha contain heavy metals?

Not necessarily, and this is exactly why testing matters. Matcha from well-managed Japanese farms with clean soils, tested before export, can return Not Detected results across all four key metals. Origin, soil quality, harvest grade, and testing rigour all determine the outcome.

Is Japanese matcha safer than matcha from other countries?

Japan's regulatory framework — the MHLW Food Sanitation Act and Positive List System — is among the most stringent in the world for agricultural products. Testing at origin before export adds a checkpoint that most other producing countries do not require. Independent consumer testing in 2025 and 2026 consistently shows Japanese-origin matcha outperforming other origins on heavy metal levels.

Does organic certification mean matcha is free of heavy metals?

No. Organic certification covers pesticide use — not soil mineral content. Heavy metals occur naturally in soil regardless of farming method. Both organic and non-organic matcha can have elevated or non-detectable heavy metal levels depending entirely on soil conditions and origin. 

What is the detection limit for heavy metals in matcha testing?

Detection limits vary by metal and methodology. Our batch testing uses atomic absorption spectrometry with detection limits of 0.3 ppm for lead, 0.05 ppm for cadmium, 0.01 ppm for mercury, and 0.2 ppm for arsenic. Any result below these thresholds returns as Not Detected.