Environmental Risk Assessment of Liquid Aluminum Sulfate Water Treatment Agent Prepared from Waste Sulfuric Acid in the Integrated Circuit Industry

Abstract

The comprehensive utilization of hazardous waste may introduce heavy metals, organic pollutants, etc., into products, resulting in secondary pollution. The environmental risk assessment method for hazardous waste resource utilization products is an important technical means of environmental management. We have established a standardized method for hazard identification, exposure evaluation and risk characterization. This study selects waste sulfuric acid generated in the integrated circuit industry as the object and investigates the use of waste sulfuric acid to react with aluminum hydroxide to produce liquid aluminum sulfate flocculant, as well as the environmental risks brought to practitioners and the potential relevant population in the sewage treatment process. By analyzing sulfuric acid and aluminum hydroxide, toxic substances such as nitrate ions, fluorides, As, Pb, Cr, Hg, Cd, etc., were identified. Through exposure scenario analysis, the exposure levels of occupational and non-occupational populations were determined. Based on the dose–response relationship data in the IRIS database of the United States and the carcinogenic and non-carcinogenic data of skin contact routes, it was suggested that chromium and its compounds were the main contributors to carcinogenic risk, and cadmium, its compounds, and mercuric chloride were the contributors to the non-carcinogenic risk. The total carcinogenic risk to human health in occupational populations was 5.31 × 10⁻⁵, and the total non-carcinogenic risk was 8.80 × 10⁻¹. The total carcinogenic risk to human health in non-occupational populations was 1.73 × 10⁻¹⁵, and the total non-carcinogenic risk was 1.23 × 10⁻¹¹. Based on this research, it is clear that the production of liquid aluminum sulfate flocculants from waste sulfuric acid generated in the integrated circuit industry has a low impact on occupational and other populations during use, and the environmental risks generated by this product are acceptable even under the most dangerous conditions.

1. Introduction

With the continuous development of industrial production in China, the pressure of resource scarcity and environmental pollution continues to intensify [1]. Hazardous waste, due to its toxic, infectious, flammable, reactive, or corrosive properties, has always been a key focus in China’s solid waste pollution control [2,3,4].

Due to the complex composition of hazardous waste and the uneven operational management and technical levels, it is difficult to fully and accurately grasp the characteristics of hazardous waste [5,6]. This leads to inadequate pollution prevention measures during the comprehensive utilization process, which could very likely result in “secondary pollution [7,8,9].” The environmental risks associated with improper comprehensive utilization may indirectly manifest through utilization products, where heavy metals such as chromium and lead may enter the environment and food chain via these products, posing significant risks to environmental safety and human health [10]. For example, waste sulfuric acid was used to produce fertilizers like phosphate, ammonium sulfate, magnesium sulfate, and organic fertilizers, which contained heavy metals such as copper, cadmium, zinc, chromium, lead, and arsenic. This leads to harmful substances entering the soil with the fertilizers, causing significant heavy metal pollution in farmland [11,12]. Industrial salt containing pesticide components used as road de-icing agents can easily lead to water pollution [13]. Additionally, some products contain impurities that may react with other raw materials at comprehensive utilization units. If the seller does not inform buyers about the main impurities and prohibited substances in the quality-inspection report, it can easily trigger safety risks.

Therefore, a method is needed to evaluate the risks associated with comprehensive utilization, clearly identifying environmental risks during the use of its products, providing a foundation for guiding the application of these products [14,15,16,17].

As an analysis, prediction, and evaluation process, environmental risk assessment comprises a wide range of qualitative, quantitative, and semi-quantitative evaluation techniques. Many scholars have conducted risk assessments on the emission of pollutants during the utilization and disposal of typical solid waste using relevant mathematical and statistical analysis methods. In order to accurately describe and reflect the exposure pathways and dose–response relationships of chemical substances, scholars have constructed several chemical substance toxicity databases based on a large number of toxicology experiments and have developed a series of prediction models and computer simulation software to simulate the migration, transformation, and exposure pathways of pollutants in environmental media. These databases and evaluation models are an integral part of population health risk assessment methods.

In order to promote the comprehensive utilization of hazardous waste, based on environmental risk research, the Standardization Administration of China has organized research on the national standard “General principles for environmental risk assessment of products from hazardous wastes comprehensive utilization” (Standard Plan Number: 20220494-T-303). At present, the standard has been drafted for approval and is about to be issued. In this standard, we establish the requirements for the evaluation procedure, hazard identification, exposure evaluation, hazard characterization, risk characterization, uncertainty analysis, risk benchmark, evaluation results, and evaluation report preparation for the environmental risk assessment of hazardous waste comprehensive utilization products. The evaluation procedure for health risks in this standard consists of four steps: hazard identification, health exposure evaluation, health toxicity evaluation, and health risk characterization, which is the foundation of this work.

1.1. Comprehensive Utilization of Waste Sulfuric Acid of Integrated Circuits

Integrated circuits are the core components of electrical and electronic devices, as well as information technology products. The production of integrated circuits generates a large amount of hazardous waste, primarily including waste acid, waste mineral oil, and organic solvent waste, copper-containing waste, and waste alkali, with waste acid being the most significant category [18]. Most of the waste acid produced by the integrated circuit industry consists of relatively simple components, with low proportions of mixed acids. Therefore, comprehensive utilization is the main approach for handling and disposing of waste acid generated by the integrated circuit industry [19,20].

Chip cleaning is one of the critical steps in integrated circuit manufacturing, primarily using acid solutions to remove oil and dust from the chip surface. This process generates hazardous waste acids. The types of waste acids produced during chip cleaning mainly include waste sulfuric acid, nitric acid, hydrofluoric acid, and phosphoric acid, with waste sulfuric acid being the most common. Waste sulfuric acid contains 60% to 70% sulfuric acid and also includes small amounts of hydrogen peroxide and other impurities. The main methods for utilizing waste sulfuric acid include using it as an acidic cleaning agent for object surfaces in a cascading manner, purifying waste sulfuric acid to use as a substitute raw material, and producing inorganic salts from waste sulfuric acid, such as aluminum sulfate flocculants for wastewater treatment, which is another important approach to utilizing waste sulfuric acid.

Flocculation plays a crucial role in wastewater treatment, directly impacting the quality of the final effluent. Aluminum sulfate flocculant [21], one of the most common flocculants, requires large amounts of sulfuric acid as raw material for production. The integrated circuit industry generates substantial amounts of waste sulfuric acid. On one hand, due to its high sulfur content, it urgently needs comprehensive utilization; on the other hand, as hazardous waste, waste sulfuric acid contains heavy metals and harmful components with different compositions from those in industrial-grade sulfuric acid. Whether the products from its comprehensive utilization will have adverse effects on surrounding populations and the ecological environment during use must be assessed through environmental risk evaluation to determine if the risks are acceptable [22,23].

1.2. Evaluation Purpose

Due to unclear exposure scenarios and environmental risk benchmarks, the environmental risk assessment of water treatment agents prepared from waste sulfuric acid is a missing link in specific management work. In this study, we established a method for environmental risk assessment of hazardous waste resource products. Selecting waste sulfuric acid generated in the integrated circuit industry as the research object, we evaluated the potential environmental risks generated during the use of polymeric aluminum sulfate prepared from this waste sulfuric acid.

1.3. Evaluation Method

According to the national standard we are developing, when conducting exposure assessments, potential exposure scenarios should be analyzed based on the possible uses of hazardous waste comprehensive utilization products, and information such as the relative orientation, distance, and activity mode of nearby populations, organisms, or species should be investigated to determine the evaluation receptor.

The exposure assessment should include evaluating all exposure pathways of the receptor to all exposure scenarios of comprehensive hazardous waste utilization products. For exposure scenarios with multiple exposure pathways, unless there is sufficient evidence to prove that a certain exposure pathway does not exist or the environmental risk of that exposure pathway is acceptable, direct exposure through oral ingestion, inhalation through respiration, and skin contact, as well as indirect exposure through environmental media (water, soil, atmosphere, sediment, particulate matter, etc.) and the food chain, should be comprehensively considered.

The population that may be exposed to harmful substances in the comprehensive utilization products of hazardous waste is usually divided into occupational groups using comprehensive utilization products, consumer groups, and groups indirectly exposed through environmental media and the food chain. Occupational groups should evaluate the risk of harmful substances based on their exposure during adulthood; Consumers and those indirectly exposed through environmental media and the food chain should consider the exposure of the general population and sensitive populations (including children and the elderly), respectively, and evaluate the risk of harmful substances.

This study evaluates the liquid aluminum sulfate flocculant produced from the comprehensive utilization of waste sulfuric acid generated in the integrated circuit industry. This case will assess the environmental risks associated with the use of the flocculant.

2. Experimental

2.1. Basic Information and Data

In 2019, the LinGang New Area of the Pilot Free Trade Zone was established in Shanghai, which is a comprehensive industrial base for integrated circuits in China and a core industrial agglomeration area with international influence. Currently, 40 integrated circuit enterprises have settled in. As the leading industry in this area, integrated circuits generate a large amount of waste acid during the production process of enterprises in the park, which needs to be disposed of in an environmentally friendly manner.

Shanghai Chengtou Xinggang Environmental Technology Development Co., Ltd. (hereinafter referred to as “Xinggang”) is the only enterprise in Shanghai that integrates solid wastewater land transportation, terminal comprehensive disposal, water area cleaning and protection, resource recovery and utilization, and hazardous waste treatment and disposal.

Through component analysis, we found that the heavy metal content in the waste acid from integrated circuit companies in the LinGang New Area is below the corresponding limit values for premium grades in China National Standard GB/T 534-2014 [24], making it suitable as raw material for producing aluminum sulfate and other water treatment agents.

The annual output of liquid aluminum sulfate flocculant produced from the resource recovery of waste sulfuric acid in this study is 62,271 t/a, all of which is used at the Bailonggang Wastewater Treatment Plant located in Pudong New Area, Shanghai. The plant serves a population of about 7,000,000 people and currently has a treatment capacity of 2.8 million t/d, accounting for one-third of Shanghai’s urban wastewater treatment capacity. It is the largest wastewater treatment plant in China and Asia, consuming approximately 200 t/d of liquid aluminum sulfate flocculant.

2.1.1. Hazardous Waste Information

The waste sulfuric acid in this case is produced in the integrated circuit-cleaning process of Semiconductor Manufacturing International Corporation and Hua Hong Semiconductor Limited. The source is stable, and the annual production scale is about 20,000 t. The waste acid is mainly waste sulfuric acid, and the content of heavy metals, according to the test data of atomic absorption spectroscopy, is very low, as shown in Table 1.

Table 1. Heavy metal content in waste sulfuric acid.

Vender	Heavy Metal or Metalloid Content (w/%)
	Arsenic	Cadmium	Chromium	Lead	Iron	Mercury
1	ND	1.00 × 10−8	5.00 × 10−7	4.00 × 10−7	1.37 × 10−5	1.00 × 10−8
2	2.00 × 10−7	2.00 × 10−8	1.20 × 10−6	8.00 × 10−7	2.32 × 10−5	ND
3	6.00 × 10−7	2.00 × 10−8	8.20 × 10−6	3.00 × 10−7	1.13 × 10−4	ND
4	5.00 × 10−7	2.00 × 10−8	2.00 × 10−7	1.00 × 10−6	1.27 × 10−5	ND

Note: “ND” indicates not detected.

According to the control requirements of hazardous waste entering the plant, Xinggang will sample and test each batch of waste acid entering the plant. The quality control requirements of waste acid entering the plant are determined according to the control standards for heavy metals in the China National Standard GB 31060-2014 [25], as shown in Table 2. Waste acid exceeding the requirements for entering the plant will not be admitted.

Table 2. Qualitative control requirements for incoming waste acid.

Ingredient (w/%)
iron	arsenic	lead	cadmium	mercury	chromium	water-insoluble
≤1.50 × 10−1	≤3.00 × 10−4	≤9.00 × 10−4	≤3.00 × 10−4	≤3.00 × 10−5	≤9.00 × 10−4	≤5.00 × 10−2

2.1.2. Process of Preparing Water Treatment Agent from Waste Sulfuric Acid

The comprehensive utilization process of waste acid adopts the acid–base neutralization method. The main process is to use the reaction between waste sulfuric acid and aluminum hydroxide to produce liquid aluminum sulfate. The chemical reaction equation is as follows:

3H₂SO₄ + 2Al(OH)₃ + 12H₂O = Al₂(SO₄)₃•18H₂O

There are 10 reactors (8 in use and 2 in reserve) in the production line of this case. The reaction time of each batch of products is 2.5 h, and 4 batches of products can be produced every day with an output of about 52 t per batch and an annual production time of 3000 h. The liquid aluminum sulfate products are temporarily stored in 6200 m³ storage tanks in the finished product and raw material storage tank area for sale.

2.2. Raw and Auxiliary Materials

The main components and the physical and chemical properties of raw and auxiliary materials in this case are shown in Table 3 and Table 4.

Table 3. Main raw and auxiliary material consumption.

Number	Material	Shape and Properties	Specifications	Application Amount
1	Waste sulfuric acid	liquid	60–70%	20,000 t/a
2	Sulfuric acid (industrial grade)	liquid	98%	80 t/a
3	Aluminum hydroxide	solid body	/	7589 t/a

Table 4. Physical and chemical properties of the main raw and auxiliary materials.

Order Number	Name	Characteristic	Toxicity
1	Sulfuric acid	Transparent and colorless oily liquid, density of 1.841 g/cm3, melting point of 10.46 °C, boiling point of 210~338 °C, flash point of 11 °C	LD50: 2140 mg/m3 (rat oral)
2	Aluminum hydroxide	The density of the white amorphous powder is 2.40 g/cm3, it is insoluble in water, and its melting point is 300 °C	/

The material balance for the production process of aluminum sulfate water treatment agent from waste sulfuric acid is shown in Table 5.

Table 5. Material balance of the production process of aluminum sulfate.

Entry	kg/Batch	t/a	Outgoing	kg/Batch	t/a
Waste sulfuric acid	16,666.667	20,000	7.8% liquid aluminum sulfate	51,892.500	62,271
Aluminum hydroxide	6324.167	7589	sulfuric acid mist	0.010	0.012
water	30,151.835	36,182.202	residual	250.000	1500
			steam	0.032	0.038
			stive	0.127	0.152
subtotal	53,142.669	63,771.202	subtotal	53,142.669	63,771.202

2.3. Products

The finished liquid aluminum sulfate produced in this case meets the China National Standard GB 31060-2014 [25], as shown in Table 6.

Table 6. Quality control requirements for liquid aluminum sulfate products.

Ingredient (w%)
Fe	As	Pb	Cd	Hg	Cr	Water-Insoluble	Alumina	pH
≤5.00 × 10−2	≤1.00 × 10−4	≤3.00 × 10−4	≤1.00 × 10−4	≤1.00 × 10−5	≤3.00 × 10−4	≤5.00 × 10−2	≥7.8	≥ 3 (1% aqueous solution)

3. Evaluation Methodology

3.1. Hazard Identification

Identification of Harmful Substances

The harmful substances in liquid aluminum sulfate products are preliminarily identified. According to the raw and auxiliary materials used in production shown in Table 3, the main components and contents of waste sulfuric acid are shown in Table 7, which were determined according to the corresponding Chinese national standards [25,26,27,28,29,30].

Table 7. Detection results of main components of waste sulfuric acid.

Determined Parameter	Unit	Value	Testing Standard
water-insoluble	%	<1.00 × 10−3	GB/T 31060-2014 [25]
pH Value (1% aqueous solution)	/	0.40	GB/T 31060-2014 [25]
NO3−	mg/kg	<10	GB/T 35496-2017 [26]
PO43−	mg/kg	<10	GB/T 9727-2007 [27]
Cl−	mg/kg	<10	GB/T 3050-2000 [28]
F−	mg/kg	<10	GB/T 21057-2007 [29]
purity	w%	65.36	GB/T 625-2007 [30]
Fe	w%	<1.00 × 10−4	GB/T 625-2007 [30]
As	w%	<1.00 × 10−4	GB/T 625-2007 [30]
Pb	w%	<1.00 × 10−4	GB/T 625-2007 [30]
Hg	w%	<1.00 × 10−4	GB/T 625-2007 [30]
Cd	w%	<1.00 × 10−4	GB/T 625-2007 [30]
Cr	w%	<1.00 × 10−4	GB/T 625-2007 [30]

According to China National Standards, the main components and contents of 98% industrial sulfuric acid (GB 534-2014) [24] and aluminum hydroxide products (GB/T 4294-2010) [31] are shown in Table 8 and Table 9.

Table 8. Composition of concentrated sulfuric acid.

Determined Parameter	Metric
	Superior Products	First Class Products	Qualified Products
sulfuric acid w/%≥	92.5 or 98.0	92.5 or 98.0	92.5 or 98.0
ash content w/%≤	0.02	0.03	0.10
Fe w/%≤	0.005	0.010	-
As w/%≤	0.0001	0.001	0.01
Pb w/%≤	0.005	0.02	-
Hg w/%≤	0.001	0.01	-

Note: The “-” in the index indicates that this item is not included in the technical requirements of this type of product.

Table 9. Composition of aluminum hydroxide.

Series of Products	Chemical Composition (Mass Fraction) b/%				Physical Property
	The Impurity Content Is Not Greater Than			Burn-Off (Decomposition)	Moisture (Adhering Water)/% Is Not Greater Than
	SiO2	Fe2O3	Na2O
AH-1 a,c	0.02	0.02	0.40	34.5 ± 0.5	12
AH-2 c	0.04	0.02	0.40	34.5 ± 0.5	12

^a When used as raw material for dry alumina production, the water content (attached water) should not be greater than 6%, and the mass fraction of particles smaller than 45 μm should not be greater than 15%. ^b Chemical composition is calculated according to the dry basis after drying at 110 °C ± 5 °C for 2 h. ^c Heavy metal elements (Cd + Hg + Pb + Cr³⁺ + As) should not be analyzed routinely by the supplier, but their content should be monitored.

Based on the raw materials and chemical process, we infer that these substances may be contained in the liquid aluminum sulfate, as shown in Table 10.

Table 10. List of possible substances in liquid aluminum sulfate flocculant.

Number	Class	Hazardous Substance	CAS Number
1	Acids	sulfuric acid	7664-93-9
		hydrogen nitrate	7697-37-2
		ortho-phosphoric acid	7664-38-2
		hydrochloric acid	7647-01-0
		hydrofluoric acid	7664-39-3
		arsenic acid	7778-39-4
2	F	fluoride	16984-48-8
3	Iron and its compounds	iron	7439-89-6
		ferric sulfate	10028-22-5
		ferric nitrate	10421-48-4
		ferric phosphate	10045-86-0
		iron trichloride	7705-08-0
		iron trifluoride	7783-50-8
		ferric hydroxide	1309-33-7
4	Arsenic and its compounds	arsenic	7440-38-2
		arsenic butter	7784-34-1
		arsenous fluoride	7784-35-2
5	Aluminum and its compounds	aluminum	7429-90-5
		aluminum sulfate	10063-01-3
		aluminum nitrate	7784-27-2
		aluminum phosphide	20859-73-8
		alchlor	7446-10-0
		aluminum fluoride	7784-18-1
		alumina	1344-28-1
		aluminum hydroxide	21645-51-2
6	Lead and its compounds	lead	7439-92-1
		lead sulfate	7446-14-2
		lead nitrate	10099-74-8
		lead orthophosphate	7446-27-7
		lead tetrachloride	13463-30-4
		lead difluoride	7783-46-2
		lead tetrafluoride	7783-59-7
7	Silicon and its compounds	silicon	7440-21-3
		silicon chloride	10026-04-7
		silicon orthophosphate	12037-47-7
8	Cadmium and its compounds	cadmium	7440-43-9
		cadmium sulfate	10124-36-4
		cadmium nitrate	10325-94-7
		cadmium phosphate	13847-17-1
		cadmium chloride	10108-64-2
		cadmium fluoride	7790-79-6
9	Mercury and its compounds	mercury	7439-97-6
		mercuric sulfate	7783-35-9
		mercury nitrate	10045-94-0
		mercuric phosphate	10451-12-4
		mercury(II) chloride	7487-94-7
		mercury difluoride	7783-39-3
10	Chromium and its compounds	chromium	7440-47-3
		chromic sulfate	10101-53-8
		chromic nitrate	13548-38-4
		chromium(III) phosphate	7789-04-0
		chromium trichloride	1333-82-0
		chromium trifluoride	7788-97-8

The identification results of harmful substances in liquid aluminum sulfate products are shown in Table 11.

Table 11. Identification results of harmful substances in liquid aluminum sulfate products.

Number	Hazardous Substance	CAS Number
1	nitrate	14797-55-8
2	chloride ion	16887-00-6
3	fluoride	7782-41-4
4	arsenic	7440-38-2
5	arsenic acid	7778-39-4
6	arsenic trichloride	7784-34-1
7	aluminum fluoride	7784-18-1
8	lead	7439-92-1
9	lead orthophosphate	7446-27-7
10	lead difluoride	7783-46-2
11	cadmium	7440-43-9
12	cadmium sulfate	10124-36-4
13	cadmium chloride	10108-64-2
14	cadmium fluoride	7790-79-6
15	mercury	7439-97-6
16	mercuric chloride	7487-94-7
17	chromium	7440-47-3

3.2. Sampling and Testing

In this study, liquid aluminum sulfate is a comprehensive utilization product in the stable production period, and the output of each batch is about 52 t. The detection of relevant substances in this study was carried out using universal chemical analysis methods; for example, the harmful substances in the liquid aluminum sulfate were determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Atomic Absorption Spectroscopy (AAS), etc., with the corresponding China national standards [26,27,28,29,30,31,32], as shown in Table 12.

Table 12. Test results of harmful substances in liquid aluminum sulfate.

Number	Hazardous Substance	Concentrations/(mg/L)	Test Method
1	nitrate radical	3.21 × 10−6	GB/T 35496-2017 [26]
2	chloride ion	3.21 × 10−6	GB/T 3050-2000 [28]
3	fluoride	3.21 × 10−6	GB/T 3050-2020 [28]
4	Arsenic and its compounds	<1.00 × 10−7	GB/T 625-2007 [30]
5	aluminum fluoride	/	GB/T 4702.5-2008 [32]
6	Lead and its compounds	2.00 × 10−6	GB/T 625-2007 [30]
7	Cadmium and its compounds	<1.00 × 10−6	GB/T 625-2007 [30]
8	corrosive sublimate	2.00 × 10−6	GB/T 625-2007 [30]
9	Chromium and its compounds	<1.00 × 10−6	GB/T 625-2007 [30]

Note: “/” is below the detection limit.

3.3. Exposure Evaluation

3.3.1. Exposure Pathway and Receptor Analysis

Liquid aluminum sulfate in this study is mainly used as a flocculant for water treatment. According to the common exposure scenarios of hazardous waste comprehensive utilization products, its use is determined as a flocculant for water treatment and sewage treatment.

The main exposure mode and receptor in this case are as follows.

• Exposed scenario 1: Direct exposure: when used as a flocculant for sewage treatment, there may be occupational exposure risks of splashing and leakage to workers’ skin during the process of feeding materials.
• Exposure scenario 2: Indirect exposure: Flocculants are discharged into rivers and other water bodies by sewage treatment plants, and human beings may be at risk of skin contact when swimming in rivers.
• Exposed scenario 3: Indirect exposure: The flocculant follows the discharge of sewage treatment plant into the Yangtze River, which may pose potential ecological risks to aquatic organisms in the Yangtze River.

3.3.2. Health Exposure Assessment

• Determination of exposure concentration

In this study, the most adverse factors of liquid aluminum sulfate products in three exposure scenarios are considered. For all not-detected harmful substances, we take the detection limits as their content during the calculation.

In exposure scenario 1, the most adverse condition is that the liquid aluminum sulfate flocculant is directly sprayed on the skin of workers, and the exposure concentration is the concentration of the product of liquid aluminum sulfate flocculant.

In exposure scenario 2, according to the operational data, the dosage of liquid aluminum sulfate flocculant in this case is 7.00 × 10⁻⁵ t/t wastewater. At the same time, it is assumed that the most unfavorable condition of exposure scenario 2 is that the flocculant is not lost and all the effluent from the sewage treatment plant enters the river, and the dilution effect of river water on the effluent is not considered. Under the above assumptions, we take the concentration of liquid aluminum sulfate in the effluent as the exposure concentration.

In exposure scenario 3, the most unfavorable condition is that the flocculant content discharged into the Yangtze River is not diluted, and the exposure concentration is calculated according to the concentration of liquid aluminum sulfate in the effluent.

According to the above exposure conditions of scenarios 1~3, the exposure concentration of harmful substances in the three exposure scenarios is estimated as shown in Table 13.

Table 13. Exposure concentration of harmful substances in each exposure scenario.

Number	Hazardous Substance	Exposure Concentration/(mg/L)
		Expose Scenario 1	Expose Scenario 2	Expose Scenario 3
1	nitrate radical	3.21 × 10−6	2.25 × 10−4	2.25 × 10−4
2	chloride ion	3.21 × 10−6	2.25 × 10−4	2.25 × 10−4
3	fluoride	3.21 × 10−6	2.25 × 10−4	2.25 × 10−4
4	Arsenic and its compounds	1.00 × 100	3.00 × 10−2	3.00 × 10−2
5	Lead and its compounds	2.00 × 100	6.00 × 10−2	6.00 × 10−2
6	Cadmium and its compounds	1.00 × 100	3.00 × 10−2	3.00 × 10−2
7	corrosive sublimate	1.00 × 10−1	3.00 × 10−3	3.00 × 10−3
8	Chromium and its compounds	1.00 × 100	3.00 × 10−2	3.00 × 10−2

2.

Calculation of exposure

According to the upcoming China National standard “General principles for environmental risk assessment of products from hazardous wastes comprehensive utilization” (Standard Plan Number: 20220494-T-303), the exposure amount of harmful substances in each exposure scenario is calculated with formula (1) in this study. The calculation formula is as follows:

$$AD{D}_{der}={\displaystyle \frac{C\times CF\times AF\times SA\times ABS\times EF\times ED}{BW\times AT}}$$

(1)

In the formula, ADD_der—is the average daily exposure of skin to harmful substances, mg/(kg•d);

• C—Concentration of harmful substances, mg/kg;
• CF—Conversion factor, kg/mg;
• AF—Skin adhesion factor, mg/cm²;
• SA—Skin contact area, cm²/event;
• ABS—Skin absorption coefficient, dimensionless;
• EF—Exposure frequency, event/a.
• ED—Exposure period, a;
• BW—Body weight, kg;
• AT—The average time, d.

According to the US Environmental Protection Agency’s Exposure Parameter Manual, Integrated Risk Information System, The Provisional Reviewed Toxicity Values and the Summary Table of Regional Screening Levels, and the China standard WS/T 777 [33], the exposure parameters selected in this case are shown in Table 14.

Table 14. Exposure parameters in the case described in this paper.

Parameter	Meaning	Unit	Reference Value
			Professional People	Non-Occupational
C	Concentration of chemicals in a liquid	mg·L−1	measured value	measured value
CF	conversion factor	L·cm−3	1 × 10−3	1 × 10−3
SA	Skin contact area	cm2	1200	16,000
PC	Skin permeability coefficient	cm·h−1	1200	16,000
EF	Frequency of exposure	d·a−1	225	9.8 × 10−6
ED	Exposure period	a	30	70
ET	open-assembly time	h·d−1	0.25	0.086
BW	middleweight	kg	61.9	61.9
AT carcinogenic	Average lifetime exposure time	d	25,550	25,550
AT-not carcinogenic	Average contact time	d	10,950	25,550

According to Formula (1) and the recommended exposure parameters in Table 14, the exposure results of the occupational population in Exposure Scenario 1 and the non-occupational population in Exposure Scenario 2 are shown in Table 15.

Table 15. Calculation results of exposure.

Number	Hazardous Substance	Average Daily Exposure of Occupational Population ADD/mg/(kg•d)		Average Daily Exposure of Non-Occupational Population ADD/mg/(kg•d)
		Carcinogenic	Non-Carcinogenic	Carcinogenic	Non-Carcinogenic
1	nitrate radical	4.11 × 10−6	9.59 × 10−6	1.34 × 10−16	1.34 × 10−16
2	chloride ion	4.11 × 10−6	9.59 × 10−6	1.34 × 10−16	1.34 × 10−16
3	fluoride	4.11 × 10−6	9.59 × 10−6	1.34 × 10−16	1.34 × 10−16
4	arsenic and its compounds	1.28 × 10−6	2.99 × 10−6	4.18 × 10−17	4.18 × 10−17
5	lead and its compounds	3.34 × 10−7	7.80 × 10−7	1.09 × 10−17	1.09 × 10−17
6	cadmium and its compounds	1.28 × 10−6	2.99 × 10−6	4.18 × 10−17	4.18 × 10−17
7	corrosive sublimate	1.73 × 10−7	4.04 × 10−7	5.66 × 10−18	5.66 × 10−18
8	chromium and its compounds	2.56 × 10−6	5.97 × 10−6	8.36 × 10−17	8.36 × 10−17

3.

Health toxicity evaluation

We calculated the toxicological parameters based on the dose–response relationship data in the US IRIS database, and the carcinogenic and non-carcinogenic data for dermal exposure are shown in Table 16.

Table 16. Toxicological parameters of harmful substances.

Number	Hazardous Substance	CAS Number	Carcinogenic SF/((kg·d)·mg−1)	Non-Carcinogenic RfD/(mg·kg−1·d−1)
1	nitrate radical	14797-55-8	/	1.60 × 100
2	chloride ion	16887-00-6	/	/
3	fluoride	7782-41-4	/	6.00 × 10−2
4	Arsenic and its compounds	7440-38-2	1.50 × 100	3.00 × 10−4
5	lead orthophosphate	7446-27-7	8.50 × 10−3	/
6	Cadmium and its compounds	7440-43-9	/	5.00 × 10−6
7	corrosive sublimate	7487-94-7	/	2.10 × 10−6
8	Chromium and its compounds	7440-47-3	2.00 × 101	7.50 × 10−5

Note: “/” indicates no related parameters.

3.4. Risk Characterization

Health Risk Characterization

According to the upcoming China National standard “General principles for en-vironmental risk assessment of products from hazardous wastes comprehensive utili-zation” (Standard Plan Number: 20220494-T-303), we calculate the carcinogenic risk characterization value and non-carcinogenic risk characterization value for this case with Formulas (2) and (3).

The calculation formula is as follows:

$$CR=AD{D}_{der}\times SF$$

(2)

The formula includes the following symbols.

CR—The threshold effect of the carcinogenic risk characterization value is dimensionless;

ADD_der—Daily exposure to harmful substances by skin contact, mg/(kg•d);

SF—Carcinogenic slope factor, kg•d/mg.

$$HQ={\displaystyle \frac{AD{D}_{der}}{RfD}}$$

(3)

The formula includes the following symbols.

HQ—Non-carcinogenic risk characterization value with threshold effect, dimensionless;

ADD_der—Daily exposure to harmful substances by skin contact, mg/(kg•d);

RfD—Reference dose of harmful substances, mg/(kg•d).

The calculation results of carcinogenic and non-carcinogenic risk indicators for occupational exposure in case 1 and non-occupational exposure in case 2 are shown in Table 17.

Table 17. Carcinogenic and non-carcinogenic risk characterization values for hazardous substances.

Number	Hazardous Substance	Risk Characterization Values of Occupational Population		Risk Representation Value of Non-Occupational Population
		Cancer Risk CR	Non-Carcinogenic HQ	Cancer Risk CR	Non-Carcinogenic Risk HQ
1	nitrate radical	/	5.99 × 10−6	/	8.38 × 10−17
2	fluoride	/	1.60 × 10−4	/	2.24 × 10−15
3	Arsenic and its compounds	1.92 × 10−6	9.96 × 10−3	6.27 × 10−17	1.39 × 10−13
4	lead orthophosphate	2.84 × 10−9	/	9.27 × 10−20	/
5	Cadmium and its compounds	/	5.97 × 10−1	/	8.36 × 10−12
6	Mercury chloride	/	1.93 × 10−1	/	2.69 × 10−12
7	Chromium and its compounds	5.12 × 10−5	7.96 × 10−2	1.67 × 10−15	1.11 × 10−12
total amount		5.31 × 10−5	8.80 × 10−1	1.73 × 10−15	1.23 × 10−11

4. Conclusions

In this study, the total cancer risk to human health for the occupational population in Scenario 1 is 5.31 × 10⁻⁵, and the total non-cancer risk is 8.80 × 10⁻¹. Chromium and its compounds are the primary contributors to the cancer risk, while cadmium and its compounds, as well as mercury chloride, contribute to the non-cancer risk. According to the upcoming China National standard “General principles for en-vironmental risk assessment of products from hazardous wastes comprehensive utili-zation” (Standard Plan Number: 20220494-T-303), the acceptable benchmark for total cancer risk for the occupational population is 10⁻⁴, and the acceptable benchmark for non-cancer risk is 1. Therefore, the health risks to the occupational population in Scenario 1 in this case are at an acceptable level.

In this case, the total cancer risk to human health for the non-occupational population in Scenario 2 is 1.73 × 10⁻¹⁵, and the total non-cancer risk is 1.23 × 10⁻¹¹. Chromium and its compounds are the primary contributors to the cancer risk, while cadmium and its compounds, as well as mercury chloride, contribute to the non-cancer risk. The health risks to the non-occupational population in Scenario 2 of this case are at an acceptable level.

From the above research, it can be seen that the environmental risks of using the liquid aluminum sulfate flocculant produced by the comprehensive utilization of waste sulfuric acid generated in the integrated circuit industry as a wastewater treatment process are acceptable. This study also demonstrates that the use of waste sulfuric acid generated in the integrated circuit industry for the preparation of liquid aluminum sulfate flocculants is a safe and resourceful process route.