Arsenic determination in surface water samples collected around chemical industrial parks is a critical element of environmental compliance monitoring, discharge verification, and ecological risk assessment. Trace-level analysis at the microgram-per-liter level relies on internationally recognized standards such as GB, ISO, and ASTM methods, together with sensitive instrumental techniques including hydride generation atomic fluorescence spectrometry, ICP-MS, and atomic absorption spectrometry. This article summarizes the sampling, preservation, analytical, and quality control procedures that accredited third-party laboratories apply when quantifying arsenic in surface water influenced by chemical industry operations.
Technical Overview
Arsenic is a toxic metalloid that enters surface water through both natural weathering and industrial activity. In the chemical industry, potential arsenic sources include the production of arsenical pesticides and wood preservatives, the use of arsenic trioxide in glass, ceramic, and pigment manufacturing, gallium arsenide processing in semiconductor fabrication, sulfuric acid production, and stormwater runoff from legacy-contaminated plant sites. Because inorganic arsenic species, particularly arsenite As(III) and arsenate As(V), are classified as carcinogenic contaminants, strict regulatory limits apply to receiving water bodies.
- GB 3838-2002 (Environmental Quality Standards for Surface Water) sets an arsenic limit of 0.05 mg/L for water quality Classes I through III and 0.1 mg/L for Classes IV and V.
- GB 8978-1996 (Integrated Wastewater Discharge Standard) restricts total arsenic in industrial effluent to 0.5 mg/L as a first-class pollutant monitored at the workshop discharge outlet.
- The WHO guideline value for arsenic in drinking water is 10 µg/L, and GB 5749-2022 adopts the same 0.01 mg/L limit, underscoring the sensitivity required of analytical methods.
Since regulatory thresholds sit near the boundary of classical colorimetric detection, modern arsenic determination in chemical-park surface water demands method detection limits in the sub-microgram-per-liter range, rigorous contamination control, and validated matrix digestion procedures.
Testing Samples
River Water Upstream and Downstream of Discharge Points
River transects are sampled upstream of the chemical plant intake, at the effluent mixing zone, and at defined downstream intervals. Longitudinal profiling distinguishes background geogenic arsenic contributions from industrial loading and supports dilution and mass-balance calculations.
Lake and Reservoir Water Near Chemical Industrial Parks
Slow-exchange water bodies accumulate particle-reactive arsenic in sediments and can release it under reducing or eutrophic conditions. Shoreline sampling near outfalls combined with mid-lake reference points is used to map spatial gradients.
Estuarine and Brackish Receiving Waters
Where chemical effluent reaches tidal waters, elevated chloride and total dissolved solids challenge several instrumental techniques. Sampling programs account for tidal phase and salinity stratification, and method selection must address spectral and polyatomic interferences.
Stormwater Runoff and Site Drainage Channels
First-flush runoff from production areas, raw material stockyards, and legacy contaminated zones frequently carries the highest arsenic loads. Event-based composite sampling captures these episodic contributions.
Background Reference Samples
Reference samples collected from hydrologically similar but uncontaminated locations establish natural baseline concentrations, which is essential for environmental impact assessment and remediation benchmarking.
Testing Items
Testing programs are typically structured around the following arsenic-related determinations:
- Total arsenic — determined on an unfiltered, fully digested sample; this is the parameter used for regulatory comparison.
- Dissolved arsenic — determined on a 0.45 µm membrane filtrate; useful for bioavailability assessment and mobility studies.
- Particulate-bound arsenic — calculated by difference or measured directly on suspended solids and sediments.
- Arsenic speciation — separation of As(III), As(V), monomethylarsenic (MMA), and dimethylarsenic (DMA) using HPLC coupled with ICP-MS, or selective hydride generation AFS, to evaluate toxicity and transformation pathways.
- Suite analysis of associated metals and metalloids (for example antimony, selenium, mercury, cadmium, and lead) often performed in parallel for source apportionment.
Sampling and Preservation
Sampling follows the ISO 5667 series and applicable national technical regulations for surface water monitoring. Key requirements include:
- Collection into acid-washed HDPE or PTFE bottles using clean-hands techniques to avoid adventitious contamination.
- Acidification of samples for total arsenic with ultrapure nitric acid to pH below 2 immediately after collection.
- A maximum holding time of approximately 28 days for acidified total-arsenic samples stored at 4 °C in the dark.
- Speciation samples filtered in the field, not acidified, refrigerated and analyzed as soon as practicable, with chelating preservatives applied where the method permits.
- Field blanks, trip blanks, and equipment rinsate blanks accompanying each sampling campaign.
Testing Methods
Hydride Generation Atomic Fluorescence Spectrometry (HG-AFS)
HG-AFS per HJ 694-2014 is one of the most widely deployed techniques for arsenic in surface water. As(V) is pre-reduced to As(III) with potassium iodide and ascorbic acid or thiourea; sodium borohydride in alkaline solution then generates arsine (AsH3), which is swept by argon into a hydrogen flame where atomic fluorescence is measured at the 193.7 nm arsenic line. The hydride step concentrates arsenic and separates it from the matrix, yielding detection limits near 0.1 µg/L with excellent tolerance to dissolved salts.
Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
ICP-MS in accordance with ISO 17294-2, HJ 700-2014, and ASTM D5673 enables simultaneous multi-element determination with detection limits of roughly 0.01 to 0.1 µg/L for arsenic. The principal interference, the polyatomic ion formed from argon and chlorine at mass 75, is controlled using helium collision-mode kinetic energy discrimination or oxygen reaction-cell mass shift to the arsenic oxide ion at mass 91. Internal standards such as germanium, rhodium, or indium correct for drift and matrix suppression.
Hydride Generation Atomic Absorption Spectrometry (HG-AAS)
ISO 11969 describes hydride generation AAS, in which generated arsine is thermally decomposed in a heated quartz tube and measured by atomic absorption. The technique achieves detection limits on the order of 1 µg/L and provides a robust single-element option for laboratories equipped with AAS instrumentation.
Graphite Furnace Atomic Absorption Spectrometry (GF-AAS)
ASTM D2972 covers atomic absorption procedures for arsenic in water, including electrothermal atomization. Matrix modifiers such as palladium or nickel nitrate stabilize arsenic during pyrolysis and permit detection limits near 1 µg/L, suitable for routine compliance-level workloads.
Silver Diethyldithiocarbamate Spectrophotometry (DDTC-Ag)
GB 7485-87 specifies the classical colorimetric method: arsine generated from the acidified sample is absorbed into a silver diethyldithiocarbamate solution, and the red complex is measured spectrophotometrically near 510 nm. With a detection limit of about 7 µg/L, the method remains useful for elevated concentrations and for laboratories requiring minimal instrumentation, although organic solvent handling must be controlled.
Sample Preparation and Digestion
Total arsenic requires complete matrix decomposition. Clear acidified waters may need only gentle heated digestion, while turbid or organic-rich samples are digested by hot-plate or microwave procedures using nitric acid with hydrogen peroxide or perchloric acid under controlled conditions. Ultrapure reagents, closed-vessel microwave digestion, and procedural blanks are essential to prevent reagent-borne arsenic contamination at trace levels.
Quality Assurance and Data Validation
Accredited third-party laboratories operating under ISO/IEC 17025 quality systems apply the following controls to every batch:
- Multi-point calibration with a correlation coefficient typically of at least 0.999, verified by continuing calibration checks every ten samples.
- Method blanks, field blanks, and reagent blanks to demonstrate freedom from contamination.
- Certified reference materials and laboratory control samples with recovery targets generally between 80 and 120 percent.
- Matrix spikes and matrix spike duplicates to assess suppression or enhancement in the specific water matrix.
- Parallel duplicate samples with relative deviation criteria appropriate to the concentration range.
- Annual or project-specific method detection limit verification and uncertainty evaluation.
Results below the method detection limit are reported as non-detects with the limit clearly stated, and regulatory comparisons are made on a total-arsenic basis against the applicable surface water class.
Applications
- Routine compliance monitoring of receiving water bodies around chemical industrial parks against GB 3838-2002 functional-zone targets.
- Verification of wastewater treatment performance and discharge permit conditions for arsenic-bearing effluents.
- Environmental impact assessment, construction project acceptance monitoring, and post-project verification surveys.
- Site investigation and remediation performance verification at legacy arsenic-contaminated chemical plants.
- Baseline surveys, long-term trend monitoring, and early-warning programs within regional surface water networks.
- Emergency response investigations following spills, unauthorized discharges, or reported exceedances.
- Research studies on arsenic speciation, transport, sediment exchange, and ecotoxicological risk in industrial watersheds.
FAQ
What is the regulatory limit for arsenic in surface water?
Under GB 3838-2002, the standard value for arsenic is 0.05 mg/L for water quality Classes I to III and 0.1 mg/L for Classes IV and V. The applicable class depends on the designated function of the water body, such as drinking water source protection, fisheries, or landscape and agricultural use.
Which analytical method is most suitable for trace-level arsenic in surface water?
For concentrations near or below the microgram-per-liter level, HG-AFS and ICP-MS are preferred because of their low detection limits and matrix tolerance. HG-AAS, GF-AAS, and the DDTC-Ag spectrophotometric method remain valid options for higher concentrations or simpler laboratory configurations.
How should samples be collected and preserved?
Collect samples in acid-washed polyethylene bottles using clean sampling techniques, acidify with ultrapure nitric acid to pH below 2 for total arsenic, store at 4 °C in the dark, and analyze within about 28 days. Speciation samples are filtered in the field and analyzed without acidification as soon as practicable.
What is the difference between total arsenic and dissolved arsenic?
Total arsenic is measured on the whole, digested sample and includes both dissolved and particulate-bound fractions. Dissolved arsenic is measured on the 0.45 µm filtrate and better reflects the mobile, bioavailable portion. Regulatory limits for surface water are generally compared against total arsenic.
What detection limits and turnaround times can be expected?
Typical method detection limits range from about 0.01 to 0.1 µg/L for ICP-MS, around 0.1 µg/L for HG-AFS, and roughly 1 to 7 µg/L for AAS-based and spectrophotometric methods. Standard turnaround is commonly five to ten working days, with expedited service available for compliance-critical or emergency projects.
Can arsenic speciation be determined in surface water?
Yes. HPLC coupled with ICP-MS, or selective hydride generation with AFS detection, separates As(III), As(V), and organic species such as MMA and DMA. Speciation data clarify toxicity, redox transformation, and industrial source signatures, and are increasingly requested in detailed risk assessments.