Arsenic analysis in organic fertilizers is a critical quality control procedure that protects soil health, crop safety, and human health by verifying that arsenic levels comply with national and international regulatory limits. This technical article explains the sources of arsenic contamination in organic fertilizers, the applicable standards such as GB 38400-2019 and NY 525-2021, and the analytical methods used by accredited third-party laboratories, including hydride generation atomic fluorescence spectrometry and ICP-MS. Whether you are a fertilizer manufacturer, importer, or agricultural researcher, understanding arsenic testing workflows is essential for product registration, certification, and market access.
Technical Overview
Arsenic (As) is a toxic metalloid that can enter organic fertilizer products through multiple pathways, including livestock and poultry manure containing residues of historic organoarsenical feed additives, phosphate-rock-derived minerals, industrial by-products, and contaminated compost feedstocks such as sewage sludge or food waste. Because arsenic is non-degradable and accumulates in soil, repeated application of contaminated organic fertilizer can increase the bioavailable arsenic pool, elevate arsenic uptake by crops such as rice and leafy vegetables, and potentially leach into groundwater.
Regulatory authorities worldwide have established strict heavy metal limits for fertilizers. In China, the mandatory national standard GB 38400-2019 (Ecological requirements for heavy metal pollutants in fertilizers) and the agricultural industry standard NY 525-2021 (Organic fertilizer) both set a maximum allowable arsenic content of 15 mg/kg (dry basis) for organic fertilizer products. In the European market, harmonized EN standards support the Fertilising Products framework, which applies corresponding arsenic thresholds to organic soil improvers. Arsenic analysis therefore serves as the fundamental basis for product registration, factory release, organic certification, and import-export verification.
Testing Samples
Commercial Organic Fertilizers
Fully fermented, commercially packaged organic fertilizers produced from animal manure, crop straw, food processing residues, and agricultural by-products, tested in accordance with NY 525 and GB 38400 requirements.
Bio-Organic and Compound Products
Bio-organic fertilizers containing functional microorganisms, organic-inorganic compound fertilizers, and blended products where organic intermediates may introduce variable arsenic backgrounds.
Composts and Soil Amendments
Livestock and poultry manure compost, green waste compost, food waste compost, vermicompost, biochar-amended amendments, and biosolids-based materials destined for land application.
Raw Materials and Intermediates
Incoming feedstocks such as chicken manure, pig manure, rapeseed meal, bone meal, humic acid, zeolite, and phosphate rock powder, screened to control arsenic carry-over before production.
Testing Items
Testing programs for organic fertilizers typically cover the following arsenic-related parameters:
- Total arsenic — the primary regulatory parameter limited to 15 mg/kg (dry basis) under GB 38400-2019 and NY 525-2021.
- Water-soluble and extractable arsenic — fractions that better reflect short-term mobility and phytoavailability in soil.
- Arsenic speciation — separation of inorganic As(III) and As(V), plus organic species such as monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and residual organoarsenical feed additive metabolites.
- Associated heavy metals — cadmium, lead, chromium, and mercury, which are commonly quantified in the same analytical run for complete GB 38400 compliance.
Testing Methods
Sample Preparation and Digestion
Representative samples are homogenized, dried at low temperature (typically not exceeding 60 degrees Celsius) or freeze-dried to preserve arsenic species, ground to pass a 0.5 mm sieve, and moisture-corrected for dry-weight reporting. For total arsenic, the most widely applied decomposition techniques include microwave-assisted digestion with nitric acid and hydrochloric acid (aqua regia) following ISO 12914 or EN 13650, and classical hot-plate wet digestion. Complete dissolution using nitric acid, hydrofluoric acid, and hydrogen peroxide may be employed for matrix-matched validation when silicate-rich minerals such as zeolite or biochar are present.
Instrumental Determination
Several mature techniques are available, each suited to different sensitivity and throughput requirements:
- Hydride generation atomic fluorescence spectrometry (HG-AFS) — the workhorse method in Chinese fertilizer laboratories, offering detection limits around 0.01 mg/kg, excellent selectivity, and low operating cost.
- Hydride generation atomic absorption spectrometry (HG-AAS) — a robust alternative consistent with the methodology frameworks of GB/T 23349 for arsenic in fertilizers.
- ICP-OES — suitable for multi-element screening of arsenic together with cadmium, lead, and chromium, particularly when combined with hydride generation for improved arsenic sensitivity.
- ICP-MS — the highest sensitivity and multi-element capability, with method development aligned with the measurement principles of ISO 17294-2; recommended for low-level detection, speciation coupling, and export-oriented certification.
Speciation Analysis
When information on arsenic forms is required, mild extraction using phosphate buffer or water-methanol mixtures is followed by high-performance liquid chromatography coupled with ICP-MS (HPLC-ICP-MS). This workflow distinguishes toxic inorganic arsenic from less toxic organic species and supports risk assessment of feed-additive-derived residues.
Quality Assurance and Reporting
Accredited third-party laboratories maintain full quality control chains, including method blanks, duplicate determinations, matrix spike recoveries of 80 to 120 percent, certified reference materials, and continuing calibration verification. Limits of detection and quantification are established statistically, measurement uncertainty is evaluated, and results are reported as mg/kg on a dry-matter basis with clear conformity judgments against GB 38400-2019, NY 525-2021, or destination-market EN requirements.
Applications
- Regulatory registration and factory release — demonstrating conformity with GB 38400-2019 and NY 525-2021 for fertilizer registration certificates and batch release.
- Organic and green input certification — supplying heavy metal evidence for organic input endorsement and eco-label programs.
- Import and export verification — meeting EN-based European requirements and destination-country fertilizer regulations.
- Raw material risk screening — building a supplier database of arsenic levels in manure, minerals, and processing by-products.
- Research and environmental assessment — supporting studies on arsenic accumulation in soil, transfer into crops, and remediation strategies.
FAQ
Why is arsenic found in organic fertilizers? Arsenic originates mainly from animal manure linked to historic organoarsenical feed additives, phosphate rock impurities, contaminated compost feedstocks, and industrial by-products. Raw material screening is the most effective control measure.
What is the regulatory limit for arsenic in organic fertilizer in China? GB 38400-2019 and NY 525-2021 both limit total arsenic to 15 mg/kg on a dry basis. Always confirm the applicable limit of the destination market, as EN-based European requirements differ.
Which analytical method is most sensitive? ICP-MS offers the lowest detection limits and simultaneous multi-element capability, while HG-AFS provides an excellent balance of sensitivity, reliability, and cost for routine total arsenic determination.
Does sample drying affect results? Total arsenic is relatively stable, but excessive drying temperatures can alter arsenic species and cause loss of volatile organoarsenicals. Low-temperature or freeze-drying is essential for accurate speciation analysis.
How are results reported? Results are expressed as mg/kg arsenic on a dry-matter basis, accompanied by detection limits, quality control data, and a conformity statement against the requested standard.
How much sample is needed and how long does testing take? A representative sample of approximately 500 g to 1 kg is generally sufficient, and routine total arsenic analysis is typically completed within five to ten working days at accredited third-party laboratories.