What Is Azoxystrobin?

Azoxystrobin is a broad-spectrum agricultural fungicide used to control fungal diseases on crops such as cereals, corn, soybeans, rice, potatoes, vegetables, grapes, fruit crops, nuts, ornamentals, and managed turf. It belongs to the strobilurin class of fungicides, also known as QoI fungicides because they inhibit fungal mitochondrial respiration at the quinone outside site of cytochrome b. Its effectiveness against many plant pathogens has made it one of the more widely detected modern fungicides in agricultural watersheds.

In drinking water, azoxystrobin is mainly a concern where surface water or shallow groundwater is influenced by pesticide application. It is not added intentionally to drinking water and is not normally associated with plumbing corrosion, treatment plant chemicals, or natural geology. Its presence usually indicates an agricultural source pathway, such as runoff after rainfall, irrigation return flow, tile drainage, field erosion, spray drift into nearby water bodies, or leaching through permeable soils.

Azoxystrobin has moderate persistence and enough mobility to be transported from treated land to water under certain conditions. It is less mobile than nitrate but more likely to appear in water than strongly soil-bound pesticides that rapidly degrade. Because it is used during crop growth periods and disease-pressure events, detections may be seasonal, with concentrations increasing after applications followed by storms, irrigation, or drainage flow.

PureWaterAtlas rates azoxystrobin as a medium-risk agricultural pollutant. This rating reflects its widespread use, repeated detection in agricultural surface waters, and potential to contaminate vulnerable wells, while also recognizing that typical drinking-water detections are usually at trace levels and that acute toxicity to humans is relatively low compared with some older pesticides.

Scientific Identity

Azoxystrobin is an organic synthetic pesticide with the molecular formula C₂₂H₁₇N₃O₅ and CAS number 131860-33-8. Its molecular weight is approximately 403.4 g/mol. The compound contains a methoxyacrylate functional group, a pyrimidinyl ether structure, and a cyanophenoxy group. These structural features are important because they influence its biological activity, water solubility, sorption to soil organic matter, and removal behavior during water treatment.

As a strobilurin fungicide, azoxystrobin was developed from natural antifungal compounds originally associated with wood-decaying fungi, but the commercial pesticide is a synthetic molecule designed for agricultural stability and crop protection. In fungi, it blocks electron transport in mitochondria, suppressing energy production and inhibiting spore germination and mycelial growth. That mode of action is specific to biological respiration processes, but it does not mean the compound is biologically inert to non-target organisms.

From a water-quality perspective, azoxystrobin is a dissolved and particle-associated organic micropollutant. It has low volatility, so it is not expected to be removed by aeration and is not a typical inhalation contaminant from tap water. It has modest water solubility and moderate hydrophobicity, allowing some attachment to suspended sediment and organic carbon while still permitting transport in dissolved form. Sunlight, microbial degradation, and hydrolysis can reduce concentrations over time, but degradation depends strongly on water chemistry, sunlight exposure, sediment conditions, and temperature.

How Azoxystrobin Enters Drinking Water

The primary pathway into drinking-water sources is movement from treated agricultural fields into surface water or groundwater. After azoxystrobin is sprayed on crops or applied as a seed treatment, soil treatment, foliar product, or turf fungicide, rainfall and irrigation can wash residues from leaves and soil into ditches, streams, ponds, and reservoirs. The highest runoff risk occurs when application is followed closely by heavy precipitation, when soils are saturated, when slopes drain directly to a waterway, or when vegetated buffers are absent.

Tile-drained agricultural land is a particularly important pathway in some regions. Subsurface drainage systems lower the water table and rapidly move field water into streams. Even when a compound is not extremely mobile, dissolved pesticide residues and fine particles can be transported through macropores, cracked soils, and tile lines. This can create short-lived concentration pulses in streams and reservoirs after storms that may not be captured by infrequent monitoring.

Private wells may be affected when they are shallow, poorly sealed, located downslope from treated fields, or screened in aquifers with rapid recharge from agricultural land. Sandy soils, fractured bedrock, karst limestone, gravel deposits, and irrigation-intensive areas can increase vulnerability. Old wells with cracked casing or poor sanitary seals can also allow pesticide-contaminated surface water to bypass natural soil filtration and enter the well directly.

Azoxystrobin can also reach water through non-crop uses. Golf courses, sod farms, nurseries, orchards, vineyards, and greenhouse runoff systems may use azoxystrobin-containing products. Improper mixing, loading, container rinsing, spills, or back-siphonage into farm water systems can create localized contamination. These point-source events are less common than diffuse runoff but can produce much higher concentrations near the release area.

Occurrence and Exposure

Azoxystrobin is most likely to be detected in agricultural watersheds where fungicide use is frequent and disease pressure requires repeated applications. Monitoring programs in North America, Europe, and other intensive farming regions have reported detections of azoxystrobin in streams, agricultural drainage, sediments, and occasionally groundwater. Surface-water detections are usually more common than deep groundwater detections because runoff, drainage, and spray drift are direct pathways to streams and reservoirs.

Exposure through drinking water depends on the source. A municipal system using a large reservoir may experience diluted, seasonal pulses that are reduced further by blending and treatment. A small community system drawing from a shallow river downstream of cropland may be more vulnerable during storm events. A private well near treated fields may show contamination only during certain seasons or may remain consistently low if the local aquifer receives slow but repeated recharge from agricultural land.

People usually encounter azoxystrobin as one component of a pesticide mixture, not as an isolated chemical. Agricultural water samples may also contain herbicides, insecticides, nitrate, phosphorus, sediment, and pesticide degradates. This matters because a household with detectable azoxystrobin may also have other runoff-related contaminants such as chlorothalonil, neonicotinoids, fertilizer residues, or nitrate. A single positive result should therefore prompt a broader pesticide and nutrient evaluation rather than a narrow one-compound response.

Seasonality is important. Testing immediately after the growing season, after a major storm, or after local fungicide application may produce different results than testing in winter or during dry weather. For private wells, repeated testing can help determine whether azoxystrobin is a persistent groundwater issue or a short-term surface-influence problem.

Health Effects and Risk

Azoxystrobin has relatively low acute toxicity in standard mammalian studies compared with many older agricultural pesticides, but drinking-water concern focuses on repeated low-level exposure, especially where water contains mixtures of agricultural chemicals. Toxicological evaluations have identified the liver as a target organ in animal studies at sufficiently high doses, with changes such as altered liver weight or biochemical effects used in risk assessment. Regulatory agencies use uncertainty factors to translate animal data into acceptable exposure levels for humans.

Azoxystrobin is generally not treated as a high-confidence human carcinogen in major pesticide risk assessments, and the U.S. EPA has characterized it as not likely to be carcinogenic to humans under relevant exposure conditions. However, this does not mean unlimited exposure is acceptable. Risk depends on concentration, duration, body weight, water intake, age, co-exposures, and whether the water also contains other pesticides or nitrate.

Infants, pregnant people, people with liver disease, and households relying on shallow private wells deserve extra caution when agricultural pesticide residues are detected. The concern is not usually immediate poisoning from tap water, but avoidable chronic exposure and the possibility that azoxystrobin is a marker for broader agricultural intrusion. If azoxystrobin is found together with nitrate, microbial indicators, or multiple pesticides, the overall water-safety concern increases.

Azoxystrobin is also toxic to some aquatic organisms at concentrations relevant to environmental protection, especially invertebrates, fish, and algae under certain exposure conditions. Ecological toxicity is not the same as drinking-water toxicity, but it explains why watershed managers track fungicide movement into streams and reservoirs. Protecting source water from pesticide pulses benefits both human drinking-water supplies and aquatic ecosystems.

Testing and Monitoring

Azoxystrobin requires laboratory pesticide analysis; it cannot be detected with a home test strip, basic mineral test, or standard coliform kit. The preferred approach is a targeted pesticide panel or expanded agricultural contaminant screen using liquid chromatography-tandem mass spectrometry, commonly abbreviated LC-MS/MS. Laboratories may use solid-phase extraction to concentrate the sample before instrumental analysis. Some multi-residue methods can detect azoxystrobin along with other fungicides, insecticides, herbicides, and degradates.

For private wells, testing should be performed by a certified or accredited laboratory familiar with pesticide residue analysis in drinking water. The lab should provide detection limits low enough for trace pesticide screening, often in the nanogram-per-liter to low microgram-per-liter range depending on the method and jurisdiction. Samples are typically collected in laboratory-supplied bottles, kept cold, protected from contamination, and shipped promptly. Do not collect pesticide samples in reused beverage bottles or containers that may adsorb organic chemicals.

Monitoring strategy should match the suspected source. If the well is near cropland, orchards, vineyards, turf operations, or drainage ditches, test during the local application season and again after major rainfall or irrigation events. If a first test detects azoxystrobin, confirm with a second sample and add related parameters such as nitrate, nitrite, total pesticides, selected herbicides, neonicotinoids, and basic microbial indicators if surface influence is possible.

Municipal utilities may monitor for pesticides through source-water programs, watershed surveillance, or unregulated contaminant studies, depending on national and local requirements. Because azoxystrobin concentrations can spike briefly after storms, grab samples taken only a few times per year may miss peak exposure periods. Event-based monitoring and seasonal sampling provide a more accurate picture in heavily agricultural watersheds.

Treatment Methods

Treatment for azoxystrobin is most reliable when it combines source control with a barrier appropriate for organic pesticide residues. Because azoxystrobin comes from land use, treatment at the tap does not solve the upstream problem. It only reduces household exposure. The best long-term approach is preventing the compound from entering wells, reservoirs, and recharge areas in the first place.

Source control is the preferred treatment because it protects all water uses and reduces contamination before it reaches the well or intake. Effective measures include observing label restrictions, avoiding application before heavy rain, maintaining setbacks from wells and streams, using vegetated filter strips, reducing erosion, managing tile-drain outlets, calibrating sprayers, preventing chemical spills during mixing and loading, and properly abandoning unused wells that may act as contamination conduits. Source control may fail when contamination is coming from neighboring properties, large watershed-scale use, legacy residues in sediment, or rapid preferential flow through fractured or karst aquifers.

Reverse osmosis is usually most appropriate as a point-of-use system under the kitchen sink for drinking and cooking water. This is practical because people ingest only a small fraction of household water. RO can fail if membranes are damaged, prefilters are neglected, pressure is inadequate, seals leak, or the system lacks maintenance. Whole-house point-of-entry RO is possible but expensive, wasteful, and maintenance-intensive; it is usually reserved for severe multi-contaminant problems. For azoxystrobin alone, point-of-use RO plus source control is generally more practical.

Activated carbon can be useful as either point-of-use carbon block filtration or larger granular activated carbon units, but pesticide removal must be verified. Carbon is not a permanent sink; once adsorption sites are exhausted, azoxystrobin can break through. Households using carbon for pesticide removal should choose certified devices where possible, follow cartridge replacement schedules, and retest treated water.

Regulations and Guidelines

Azoxystrobin regulation varies by country and jurisdiction. In the United States, azoxystrobin is regulated as a pesticide under federal pesticide law, including product registration, label requirements, crop tolerances, environmental risk assessment, and use restrictions. However, there is no federal Safe Drinking Water Act Maximum Contaminant Level specifically established for azoxystrobin in finished drinking water. Some U.S. agencies may use health-based screening values, pesticide benchmarks, or state-level guidance to interpret detections, but these are not the same as enforceable national drinking-water limits.

The World Health Organization has not established a widely cited individual guideline value for every registered agricultural pesticide, and azoxystrobin may not appear as a dedicated WHO drinking-water guideline in many reference lists. Where no specific WHO value exists, local regulators typically rely on national pesticide evaluations, toxicological reference doses, occurrence data, and general chemical risk-assessment methods.

In the European Union, drinking-water rules include a general parametric approach for pesticides: individual pesticides are commonly subject to a very low limit, and total pesticides are also limited. This system is not based solely on the toxicology of each pesticide; it is also a precautionary source-water protection standard. Individual country implementation, monitoring lists, enforcement procedures, and exemptions can vary. Other countries may set their own health-based values, operational screening levels, or no specific numerical limit for azoxystrobin.

Because limits and guidance values vary, a laboratory result should be interpreted using the rules applicable to the water system’s location. For private wells, there may be no routine legal monitoring requirement even when nearby public systems are monitored. Well owners in agricultural areas should use local health departments, agricultural extension services, certified laboratories, or drinking-water regulators to determine whether an azoxystrobin result requires treatment, follow-up sampling, or a broader pesticide investigation.

Related Contaminants

Frequently Asked Questions

Is azoxystrobin common in drinking water?

It is not one of the most common household drinking-water contaminants, but it is a relevant agricultural source-water contamin