Arsenic Testing for Surface Water Impacted by Chemical Industry Pollution: Methods, Standards, and A

Arsenic testing of surface water affected by chemical industry pollution is essential for regulatory compliance, ecological risk control, and the protection of downstream water users. As a Group 1 human carcinogen frequently associated with sulfuric acid production, agrochemical manufacturing, and legacy industrial discharges, arsenic must be quantified at microgram-per-liter levels using validated analytical methods. This article explains sampling protocols, key testing items, recognized standards such as GB, ISO, ASTM, and US EPA procedures, quality control requirements, and typical applications for arsenic analysis in chemically impacted surface water.

Technical Overview

Arsenic (As) is a toxic metalloid that reaches surface water bodies through treated and untreated discharges from chemical manufacturing facilities, stormwater runoff from contaminated industrial sites, leachate from solid wastes such as phosphogypsum stacks and metallurgical slag, and atmospheric deposition from roasting and combustion processes. Principal chemical industry sources include pyrite-based sulfuric acid plants, phosphate fertilizer production, historical arsenical pesticide and herbicide synthesis, chromated copper arsenate (CCA) wood preservative formulation, glass and pigment manufacturing, gallium arsenide semiconductor processing, and coal chemical operations.

In well-oxygenated surface water, arsenic exists mainly as pentavalent arsenate, which sorbs strongly to iron and manganese oxides on suspended particles. Under reducing or strongly alkaline conditions, trivalent arsenite becomes more prominent and is both more toxic and more mobile. The International Agency for Research on Cancer classifies arsenic as a Group 1 human carcinogen, linked to skin lesions and cancers of the skin, bladder, and lung. Regulatory thresholds are correspondingly strict: China's surface water quality standard GB 3838-2002 sets an arsenic limit of 0.05 mg/L for Class I–III waters and 0.1 mg/L for Class IV–V waters, while the WHO drinking water guideline value is 0.01 mg/L. Meeting these limits demands analytical techniques with low-microgram or sub-microgram per liter detection capability, rigorous contamination control during sampling, and standardized quality assurance performed by accredited third-party laboratories.

Testing Samples

Rivers and Streams Near Chemical Plants

Samples are typically collected as grab or time-weighted composites along a design that includes an upstream background station, points within and immediately downstream of the discharge mixing zone, and downstream transects to evaluate dilution and attenuation. Depth-integrated sampling may be required in deeper, well-mixed channels.

Lakes, Reservoirs, and Ponds in Industrial Parks

Standing water bodies require stratified sampling across the epilimnion, thermocline, and hypolimnion because arsenic released from anoxic sediments can accumulate in bottom waters. Shoreline seepage zones, inlet channels, and outlet structures should also be sampled to trace contaminant pathways.

Effluent-Receiving Water Bodies and Mixing Zones

Water collected near permitted outfalls verifies whether discharge concentrations comply with applicable effluent limits and whether complete mixing has occurred. Samples taken at incremental distances downstream help characterize plume behavior and calculate mass loads.

Filtered, Unfiltered, and Auxiliary Fractions

Unfiltered, acidified samples yield total recoverable arsenic for direct comparison with quality standards. Samples filtered in the field through 0.45 μm membranes provide the dissolved fraction, and the difference represents particulate-bound arsenic on suspended solids. Where source attribution is needed, bed sediment and pore water samples may be collected as supporting matrices.

Proper containers and preservation are critical at trace levels. Samples are collected into pre-cleaned, acid-washed HDPE or PTFE bottles, acidified with ultrapure nitric acid to pH below 2, held at 4 °C in the dark, and analyzed within the validated holding period, which is up to six months for acidified total metals. The dissolved fraction must be filtered before acidification. Field blanks, equipment blanks, and duplicate samples accompany each sampling campaign to demonstrate contamination control and precision.

Testing Items

The core testing program for arsenic in chemically affected surface water typically includes the following items:

• Total arsenic (total recoverable, unfiltered) — the primary compliance parameter against GB 3838-2002 or local water quality objectives.
• Dissolved arsenic (0.45 μm filtered) — indicates the bioavailable and most mobile fraction.
• Particulate arsenic — calculated as total minus dissolved, reflecting association with suspended solids.
• Inorganic arsenic speciation — determination of As(III) and As(V) to assess toxicity, redox state, and treatment options.
• Organic arsenic species — monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), usually minor in surface water but relevant near agrochemical sources.
• Supporting parameters — pH, oxidation-reduction potential, sulfate, sulfide, iron, manganese, suspended solids, and hardness, which govern arsenic mobility and assist data interpretation.

Testing Methods

Atomic Fluorescence Spectrometry (AFS)

Hydride generation AFS, specified in Chinese standard HJ 694-2014, is one of the most widely used techniques for arsenic in water. Pentavalent arsenic is first pre-reduced with a thiourea–ascorbic acid solution, then converted to arsine by potassium borohydride and carried into an argon–hydrogen flame for fluorescence measurement. Method detection limits of 0.1–0.3 μg/L comfortably support surface water compliance testing, and the technique offers low operating cost and high sensitivity.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

ICP-MS, covered by HJ 700-2014, ISO 17294-2, and US EPA Method 200.8, provides the lowest detection limits, often below 0.05 μg/L, together with simultaneous multi-element capability that allows arsenic, antimony, selenium, thallium, and heavy metals to be measured in a single run. Collision or reaction cell technology is used to resolve the polyatomic argon chloride interference at mass 75, which is particularly important for chloride-rich samples. Germanium or rhodium internal standards correct for matrix and drift effects.

Hydride Generation Atomic Absorption Spectrometry (HG-AAS)

Described in ISO 11969 and US EPA Method 7062, hydride generation AAS chemically separates arsenic from the sample matrix as arsine before atomization, delivering robust performance in high-chloride and high-sulfate waters. Detection limits near 1 μg/L are adequate for most compliance monitoring scenarios.

Silver Diethyldithiocarbamate Spectrophotometry

The classical colorimetric method in GB/T 7485 and referenced among the procedures of ASTM D2972 reduces arsenic to arsine, which is absorbed in a silver diethyldithiocarbamate solution and measured near 510 nm. With a minimum detectable concentration of approximately 7 μg/L, it remains useful in laboratories lacking instrumental techniques or for screening heavily contaminated waters.

ICP-OES for High-Concentration Samples

For accident response or grossly polluted water where arsenic reaches hundreds of micrograms per liter or higher, inductively coupled plasma optical emission spectrometry offers a wide linear range and rapid throughput, and can be paired with hot-plate or microwave digestion for total recoverable determinations.

Arsenic Speciation by HPLC-ICP-MS

When speciation is required, anion-exchange high-performance liquid chromatography coupled to ICP-MS separates As(III), As(V), MMA, and DMA under conditions that preserve the original valence state. Speciation samples must be filtered immediately, kept cold, and analyzed promptly, or stabilized using established field protocols, because redox transformations during storage can distort results.

Quality control in all methods follows ISO/IEC 17025 principles: multi-point calibration with certified reference materials, method and field blanks, laboratory duplicates with relative percent difference typically below 20 percent, matrix spike recoveries of 80–120 percent, continuing calibration verification, and periodic method detection limit studies. Participation in inter-laboratory proficiency programs provides additional confidence in reported data.

Applications

Arsenic testing data from chemically impacted surface water support a wide range of regulatory and engineering decisions:

• Routine compliance monitoring of chemical industrial parks, direct dischargers, and sewage treatment plants receiving industrial effluent.
• Environmental impact assessment and post-construction acceptance monitoring for new or expanded chemical facilities.
• Emergency response to spill events, fish kills, or discolored water, where rapid ICP-MS turnaround identifies the extent and severity of contamination.
• Verification of remediation performance after treatment measures such as ferric salt co-precipitation, lime precipitation, adsorption, or ion exchange.
• Long-term baseline and trend monitoring to detect gradual deterioration or validate recovery of historically polluted river reaches.
• Input data for ecological and human health risk assessments and for hydrodynamic water quality models.
• Environmental due diligence for land transactions and forensic source apportionment in pollution disputes.

FAQ

What is the regulatory limit for arsenic in surface water?

Under China's GB 3838-2002 standard, the arsenic limit is 0.05 mg/L for Class I, II, and III surface waters and 0.1 mg/L for Class IV and V waters. The applicable class depends on the designated use of the water body, such as drinking water source protection or agricultural and landscape use. The WHO guideline value of 0.01 mg/L applies specifically to drinking water.

Which analytical method provides the best detection capability?

ICP-MS offers the lowest detection limits, frequently below 0.05 μg/L, followed closely by hydride generation AFS at roughly 0.1–0.3 μg/L. All recognized methods are sufficiently sensitive for surface water compliance; selection depends on matrix, throughput needs, budget, and regulatory acceptance.

How should surface water samples for arsenic be preserved?

Collect samples in acid-washed HDPE or PTFE bottles, filter in the field through a 0.45 μm membrane if the dissolved fraction is required, then acidify with ultrapure nitric acid to pH below 2. Store samples at 4 °C in the dark. Properly preserved total metals samples may be held for up to six months, although speciation samples must be analyzed much sooner.

Why is arsenic speciation testing important?

Trivalent arsenite is considerably more toxic and mobile than pentavalent arsenate, and the two species respond differently to treatment technologies. Speciation data therefore improve risk assessment accuracy and guide the selection of chemical oxidation or co-precipitation steps in treatment design.

What interferences can affect arsenic results?

In ICP-MS, the polyatomic argon chloride ion at mass 75 overlaps the arsenic signal in chloride-rich samples and is controlled using collision cell mode or matrix dilution. In hydride-based methods, incomplete pre-reduction of As(V) and high nitrate or sulfide levels can suppress arsine generation, which is addressed through validated reagent protocols and matrix spike checks.

How can data quality be assured?

Engage accredited third-party laboratories operating under ISO/IEC 17025 quality systems. Reliable data packages include field and method blanks, duplicate analyses, certified reference material recoveries, matrix spike results, calibration records, and clearly stated detection limits, allowing reviewers to verify that reported concentrations are fit for regulatory decision-making.