By Dr. Brad Cavinder, Ph.D., Director of Microbiology and Amber Middlebrook, Regional Director of Business Development
As the cultivation of cannabis and hemp accelerates during peak growing seasons, so does the risk of contamination. Warmer temperatures, increased humidity, intensive agricultural activity, and compressed harvest timelines create ideal conditions for contaminants such as heavy metals, microbials, and mycotoxins to emerge and spread. For cultivators and manufacturers, understanding these seasonal risks, and responding with proactive, science-driven testing, is essential to protecting product safety, maintaining regulatory compliance, and safeguarding consumer trust.
Peak cultivation seasons, especially in outdoor grow facilities, typically coincide with environmental conditions that favor biological growth and chemical uptake. Cannabis is a known bioaccumulator, meaning it readily absorbs substances from its growing environment, including heavy metals, pesticides, and other environmental contaminants. When production scales rapidly, whether due to market growth or seasonality, even small lapses in environmental control or agricultural inputs can have outsized consequences.
At ACT LAB, operating across six states with diverse regulatory frameworks, we routinely observe seasonal patterns in contamination data. These trends underscore the importance of anticipating risk rather than reacting to failed results after harvest.
Heavy Metals: Soil and Water Matter More Than Ever
Heavy metals such as lead, arsenic, cadmium, and mercury originate primarily from soil, water, and fertilizers. During the growing season, increased irrigation and nutrient application can mobilize metals already present in soil, making them more bioavailable to plants.
Agricultural soil can accumulate heavy metals over time, particularly when phosphate fertilizers, contaminated irrigation water, or certain organic inputs are used. Even well-intentioned organic practices can introduce risk: components such as bone char, fish meal, kelp products, composts, and other biological amendments may contain trace amounts of heavy metals. While these levels may seem insignificant on their own, repeated applications or seasonal droughts followed by heavy irrigation can concentrate metals in the root zone, increasing uptake during critical growth phases.
As bioaccumulators, cannabis and hemp are actively studied for their ability to remediate contaminated soils by pulling heavy metals into plant tissue. While this trait is useful for environmental cleanup, it presents a serious challenge for cultivation, as even low-level contamination in growing media can become concentrated in the final product. For cultivators building their own soils, every component matters, and any detectable level of heavy metals in inputs can ultimately push plants beyond regulatory acceptance limits. Testing individual soil components and water sources before use is strongly recommended, as final-product thresholds are often far more stringent than allowable levels in raw materials.
Without early soil and water testing, cultivators may not detect these risks until final compliance testing, when remediation options are limited or nonexistent.
Microbials: Warmth, Humidity, and Handling Pressure
Microbial contamination, including Aspergillus, E. coli, Salmonella, and total yeast and mold, tends to spike during warmer months. Elevated temperatures and humidity create ideal conditions for microbial growth both in the field and post-harvest.
According to the Centers for Disease Control and Prevention (CDC), improper handling and environmental exposure are major contributors to microbial contamination in agricultural products. In cannabis cultivation, dense canopies, inadequate airflow, and rushed harvesting practices can trap moisture and facilitate microbial proliferation.
Post-harvest steps like drying, curing, trimming, and storage are particularly vulnerable during high-volume periods. Overloaded drying rooms or inconsistent environmental controls can quickly turn a healthy crop into a failed batch.
Mycotoxins: The Invisible Byproduct of Mold
Mycotoxins, including aflatoxins and ochratoxin A, are toxic secondary metabolites produced by certain molds, most notably species of Aspergillus. Unlike visible mold contamination, mycotoxins can persist even after the mold itself is no longer detectable, which is why they are closely regulated in many agricultural products.
In practice, however, mycotoxin failures in regulated cannabis markets, like Michigan for example, are extremely rare. Mycotoxin production typically requires a nutrient-rich, lipid-dense substrate, such as seeds, where fats and related compounds are present at much higher concentrations than in unseeded flowers or leaves. While cannabis flowers do contain some lipids, they are not nearly as conducive to mycotoxin development as seeded plant material.
Additional stressors, such as prolonged humidity, late-season rains, or delayed harvests can contribute to secondary mycotoxin production, but these factors are generally secondary to the presence of sufficient lipids. This helps explain why mycotoxin detections are more commonly observed in hemp, particularly industrial or grain-focused hemp, where seed production is intentional and environmental controls may be less stringent, compared to regulated, smokeable cannabis operations. Outdoor cultivation also carries a slightly elevated risk, as rogue male plants can pollinate crops from significant distances, potentially leading to unintended seed development.
While the overall risk of mycotoxins in commercial cannabis remains low, prevention is still essential. Once mycotoxins are present, they cannot be remediated, making sound cultivation practices, environmental control, and early monitoring the most effective safeguards.
The Value of Early and Routine Testing
One of the most effective ways to manage seasonal contamination risk is through early and routine testing before plants reach final compliance stages. Pre-harvest soil and water analysis, in-process microbial screening, and environmental monitoring allow operators to identify risks while corrective actions are still possible.
Proactive testing helps prevent:
- Failed compliance tests
- Costly product destruction
- Supply chain disruptions
- Damage to brand reputation
Data-driven cultivation decisions, supported by reliable laboratory insights, enable cannabis and hemp producers to adjust inputs, improve environmental controls, and refine handling practices throughout the season.
From Soil to Shelf: Navigating Contaminant Risks Across ACT LAB’s Network
As cultivation activity accelerates, understanding how state regulations and environmental conditions intersect with seasonal risks is critical for growers in every market. Below is a breakdown of how heavy metals, microbials, and mycotoxin contamination concerns manifest in six key U.S. cannabis states, and what cultivators should consider as environmental stressors increase during peak season.
Michigan – Bioaccumulation of Heavy Metals Plus Mold Hotspots
Michigan’s Cannabis Regulatory Agency (CRA) mandates testing for heavy metals including arsenic, cadmium, lead, mercury, chromium, nickel, and copper; microbial contaminants such as total yeast and mold, E. coli, and Salmonella; and mycotoxins like those produced by multiple Aspergillus species.
For outdoor cultivators, warm, humid Michigan summers can elevate fungal growth on dense flower canopies, while heavy natural rainfall can mobilize naturally occurring or legacy heavy metals in soil into root zones and irrigation runoff. Proper irrigation practices and environmental controls are essential to mitigate these seasonal spikes.
Outdoor growers should routinely assess soil conditions and verify that grow bags, raised beds, and containers are clean and uncontaminated prior to filling. Reusing containers or media without proper sanitation can unintentionally introduce accumulated heavy metals or microbial risks from previous seasons. Awareness of surrounding land use is equally important; neighboring agricultural operations, orchards, or municipal mosquito control programs may apply approved sprays that still pose a drift risk. Cultivators should stay informed about local ordinances and approved pesticide and insecticide lists in their area to better anticipate potential exposure pathways.
Thoughtful field design can significantly reduce contamination risk. Proper plant spacing improves airflow and lowers canopy humidity, while well-leveled land helps prevent water pooling in low areas where fungal growth is more likely to develop. Understanding local water tables, drainage patterns, and runoff behavior is also critical during periods of heavy rain, as excess surface or subsurface water can carry both microbial contaminants and heavy metals into growing areas.
These seasonal conditions increase the likelihood of both microbial contamination and heavy metal uptake, making proactive site management and monitoring essential. Aligning cultivation practices with these environmental realities is key to reducing seasonal compliance risk before plants ever reach the testing stage.
Illinois – Lower Microbial Limits and Mycotoxin Mandates
Illinois requires comprehensive testing for heavy metals, microbial contaminants, and mycotoxins across cannabis products, but it is the state’s notably strict total yeast and mold (TYM) action limits that present a particular challenge for operators. Illinois’ microbial thresholds are set lower than those in many other regulated markets. Even modest increases in environmental fungal load, often driven by seasonal humidity, dense canopy structures, or minor deviations in drying and curing conditions, can result in non-compliant results.
From a microbiological standpoint, these limits demand a higher level of environmental control, sanitation rigor, air purification, and in-process monitoring throughout cultivation and post-harvest handling. For operators, this elevates the importance of proactive microbial screening and moisture management well before final compliance testing, as small, undetected shifts in microbial growth can quickly exceed allowable thresholds under Illinois regulations.
Ohio – Mandatory Contamination Screening Across the Board
Under Ohio Administrative Code 3796:4-2-04, cannabis products must be tested for microbial contamination, mycotoxins, and heavy metals including arsenic, cadmium, lead, and mercury prior to sale, regardless of whether they are sold as plant material or manufactured products. As Ohio’s medical and adult-use markets continue to scale, increased crop density during peak production periods can elevate microbial pressure when airflow, canopy spacing, and humidity are not tightly controlled.
Warm temperatures and elevated relative humidity are known to accelerate fungal growth, increasing the risk of mold and mycotoxin formation if environmental conditions fluctuate during flowering, drying, or curing. At the same time, seasonal irrigation shifts and fertilizer inputs can mobilize heavy metals present in agricultural soils, increasing the likelihood of plant uptake in a crop with well-documented bioaccumulative properties. As a result, Ohio cultivators benefit from early soil, water, and in-process microbial testing to manage seasonal risk and avoid downstream compliance failures.
Pennsylvania – Regulatory Emphasis on Testing Accuracy
Pennsylvania’s medical cannabis program, governed by Title 28 Pa. Code Chapter 1171a and overseen by the Department of Health, mandates comprehensive quality and stability testing to ensure patient safety. All harvest batches and process lots must undergo testing by an approved laboratory prior to sale, with results documented in a Certificate of Analysis (COA). Required contaminant panels include microbiological impurities, mycotoxins, and heavy metals such as arsenic, lead, cadmium, and mercury. Stability testing is required at defined intervals, typically 1- and 3-month checkpoints for flower and up to one year for extracts, and includes repeat testing for microbial contamination, mycotoxins, heavy metals, and moisture content. Analytical methods must be validated for accuracy, precision, sensitivity, and specificity, reflecting Pennsylvania’s emphasis on defensible, reproducible testing data.
From a cultivation science perspective, Pennsylvania’s spring and fall climate presents elevated contamination risk due to warm daytime temperatures followed by cool, humid nights. These conditions promote condensation within grow houses and canopy microclimates, increasing relative humidity and water activity, which are key drivers of fungal growth and potential mycotoxin production. Species such as Aspergillus can proliferate under sustained high humidity and limited airflow, leading to elevated yeast and mold counts or mycotoxin failures at testing. Continuous monitoring of temperature, relative humidity, dew point, and moisture swings, combined with appropriate HVAC control and airflow management, is critical for mitigating seasonal contamination risk and maintaining regulatory compliance.
New York – Stringent Limits and Environmental Complexity Demand Precision
New York’s cannabis testing program, administered by the Office of Cannabis Management (OCM), is distinguished by one of the broadest and most conservative heavy-metal panels in the country, reflecting the state’s heightened environmental and public-health risk profile. In addition to arsenic, cadmium, mercury, and lead, New York uniquely requires routine testing for chromium, nickel, copper, and antimony, metals commonly associated with legacy industrial activity, urban soils, and aging water infrastructure.
New York’s environmental conditions further complicate compliance. Humid summers, frequent late-season rainfall, and wide regional variability between urban, coastal, and upstate growing areas increase the risk of fungal proliferation and mycotoxin formation, particularly for outdoor and greenhouse cultivation. At the same time, New York’s low heavy-metal thresholds mean that seasonal fluctuations in irrigation water chemistry, nutrient sourcing, or substrate composition can materially affect test outcomes. As a result, cultivators operating in New York must manage not only canopy-level humidity and airflow, but also upstream environmental inputs with exceptional precision to remain compliant in the state.
Florida – Medical Market with Broad Contamination Targets
Florida’s medical marijuana program operates under a vertically integrated, medical-only regulatory model overseen by the Florida Department of Health’s Office of Medical Marijuana Use (OMMU). While Florida’s numeric action limits and enforcement practices differ from other states, the regulatory framework mandates standardized laboratory conditions, validated analytical methods, and third-party verification to ensure consistent screening of these critical contaminant classes before products reach patients.
Florida’s growing environment presents some of the most persistent biological contamination pressure in the U.S. cannabis market. Prolonged heat, high ambient humidity, and frequent summer rainfall create near-continuous conditions favorable to fungal and bacterial growth, both indoors and in greenhouse operations. Even well-controlled facilities face challenges maintaining optimal vapor pressure deficit (VPD), airflow, and surface dryness during peak summer months. These conditions increase the risk of mold proliferation and secondary mycotoxin formation, particularly when post-harvest drying and curing environments are insufficiently controlled. As a result, Florida operators must rely heavily on robust HVAC capacity, dehumidification, and environmental monitoring to maintain compliance in a climate where microbial risk is structurally elevated year-round.
Actionable Strategies for Seasonal Risk Mitigation
When cultivation ramps up, operators can take several practical steps to reduce contamination risk:
- Test Soil and Water Early
Establish baseline heavy metal profiles before planting and re-test when changing inputs or water sources. - Control Environmental Conditions
Optimize airflow, temperature, air purification, and humidity, especially during flowering and drying, to limit microbial growth. - Implement Staggered Harvesting
Avoid overwhelming post-harvest infrastructure by spacing harvests when possible. - Enhance Sanitation Protocols
Increase cleaning frequency for tools, surfaces, and storage areas during peak activity. - Leverage In-Process Testing
Don’t wait for final compliance. Mid-cycle microbial and moisture testing can prevent downstream losses.
Protecting Quality Through Science
Seasonal cultivation surges are an opportunity, not just a risk. With informed planning and proactive testing, cultivators and manufacturers can navigate peak production periods with confidence. At ACT LAB, our multi-state footprint and scientific expertise allow us to help clients anticipate seasonal challenges and implement data-backed solutions that protect both product integrity and consumer safety.
By understanding how environmental and agricultural factors influence contamination, and acting early, operators can turn seasonal risk into a competitive advantage grounded in quality, compliance, and trust.
Ready to Protect your Crop as Cultivation Scales?
As cannabis cultivation activities scale throughout the year, growers face increased risks from microbials, heavy metals, and mycotoxins, whether operating controlled indoor facilities or outdoor and greenhouse environments exposed to variable conditions. ACT LAB partners with cultivators at every stage, from seed to sale, providing reliable testing and environmental monitoring to help identify issues early, protect crop quality, and reduce costly losses.
We believe testing goes beyond compliance as a proactive tool to safeguard your harvest and strengthen your operation in an increasingly competitive market. Connect with ACT LAB today to speak with a testing specialist and build a smarter testing strategy for your grow.
