Is It Safe to Use Round Plastic Bowls for Hot Soup?

1. Types and Characteristics of Disposable Plastic Round Bowl Materials

1.1 Common Material Classifications and Markings

• Polypropylene (PP): The preferred material in the takeaway food industry, marked as "PP5" or the number "5". Its characteristics include high temperature resistance (conventional use temperature -6℃ to 120℃, can be extended to -18℃ to 110℃ after modification), non-toxic, microwaveable, and resistant to acids and alkalis, impact resistant, and opaque or translucent. It is currently one of the safest materials.
• Polystyrene (PS): Marked as "PS6" or the number "6", commonly found in foam food containers and transparent plates. It is stable at room temperature, has high hardness and good transparency, but is easily torn. It starts to soften at 75℃, has excellent low-temperature performance, and is suitable for holding refrigerated foods such as ice cream, but not suitable for contact with high temperatures.
• Polyethylene terephthalate (PET): Marked with the number "1", mostly used in mineral water bottles and beverage bottles. It has high transparency and strong hardness, but poor heat resistance (only resistant to temperatures below 70℃). Exceeding this temperature can easily cause deformation and release harmful substances, so it should not be used for hot food.
• Other materials: Polyethylene (PE) is divided into high-density (HDPE, number "2", heat resistant 90-110℃) and low-density (LDPE, number "4", heat resistant 70-90℃); Polyvinyl chloride (PVC, number "3") has been gradually restricted due to the release of chlorides, phthalates, and other toxic substances at high temperatures.

1.2 Comparison of Heat Resistance of Different Materials

• PP material: Has the best heat resistance, with a melting point of 167℃ and a maximum heat resistance of 130℃. Experiments show that it has good thermal stability after being immersed in hot water at 60℃, 80℃, and 95℃ for 2 hours, with no significant change in dissolved residue. It is suitable for hot meals, microwave heating, and even steam cooking. PS material: Poor heat resistance, softens at 75℃, and releases styrene monomers above 80℃. In actual tests, PS6 material released long-chain alkanes after 10 minutes of contact with 100℃ boiling water, and the migration amount increased with temperature. The heat resistance limit is only 75℃, making it unsuitable for food above 70℃.
• PET material: The worst heat resistance, only 60-70℃. Exceeding this temperature not only causes rapid deformation but also releases harmful substances such as acetaldehyde. Long-term ingestion irritates the digestive tract mucosa and is completely unsuitable for hot food.
• Other materials: HDPE has a heat resistance of 90-110℃, LDPE has a heat resistance of 70-90℃, with limited applicable scenarios; PVC releases toxic substances at high temperatures and has been strictly restricted for food contact.

1.3 Safety Standards Requirements for Food-Grade Plastics

• Raw material requirements: Resins must comply with GB 4806.6 and relevant announcements, and the use of medical/industrial recycled plastics is strictly prohibited; additives must comply with GB 9685-2016 "Standard for the Use of Additives in Food Contact Materials and Products".
• Physicochemical index requirements: Total migration ≤ 10mg/dm², potassium permanganate consumption ≤ 10mg/kg, heavy metals (calculated as lead) ≤ 1mg/kg, and the total migration of aromatic primary amines must not be detectable; Bisphenol A (BPA) is prohibited in food contact materials for infants and young children, and the migration limit has been reduced from 0.6mg/kg to 0.05mg/kg.
• Labeling requirements: Must be marked with "for food contact," the temperature range of use, whether it is microwaveable, and the maximum operating temperature must be clearly stated to ensure that no harmful substances are released under the intended use conditions. 

2. Interaction Between Hot Soup Temperature and Plastic Materials

2.1 Analysis of Hot Soup Temperature Range

• Typical temperature range: The temperature of freshly prepared hot soup is mostly between 70-100℃, with hot pot broth reaching 120℃, freshly brewed tea at 80-90℃, freshly cooked dumplings/noodles at 70-80℃, and freshly served porridge at 92℃ (approximately 80℃ after 15 minutes). Hot soup served at the table is approximately 80℃ (65-70℃ when consumed).
• Temperature change pattern: High-temperature soup cools down with a "fast first, then slow" pattern. At a room temperature of 24℃, 500ml of 100℃ hot water cools to 85℃ after 5 minutes, 75℃ after 10 minutes, 70℃ after 15 minutes, and 60℃ after 30 minutes. This pattern provides a crucial reference for the safe use of round plastic bowls.

2.2 Physical and Chemical Changes of Plastic Materials at High Temperatures

• Physical changes: PS material softens at 75℃ and deforms significantly above 80℃; PET material deforms noticeably at 60-70℃; PP material remains stable below 120℃ with no significant morphological changes.
• Chemical changes: High temperatures accelerate the movement of plastic molecules, leading to the breakage of molecular chains and the release of harmful substances. PS material releases styrene monomer at high temperatures (a Class 2B carcinogen, causing short-term respiratory irritation, dizziness, and nausea, and long-term liver damage and endocrine disruption). A local sampling showed that some PS food containers exceeded the styrene migration limit by 3 times when holding 60℃ hot soup; microplastic release is a prominent issue. PP food containers holding 78℃ braised pork and 85℃ hot and sour soup for 15 minutes released 12,000 microplastics per square centimeter, while PS containers released 35,000 microplastics per square centimeter; a 2023 study in *Environmental Science & Technology* indicated that during microwave heating, each square centimeter of the container releases over 2 billion nanoplastics and 4 million microplastics.

2.3 Mechanisms and Influencing Factors of Harmful Substance Leaching

• Temperature: This is the most critical influencing factor. For every 10°C increase in temperature, the migration rate of chemical substances increases by 2-3 times. At 25°C, 40°C, and 55°C, the carcinogenic risks of leached PAEs (phthalates) to humans are 1.09×10⁻⁸, 4.52×10⁻⁸, and 1.83×10⁻⁷, respectively, while the non-carcinogenic risks are 1.10×10⁻⁴, 3.62×10⁻⁴, and 1.21×10⁻³, respectively. The risk increases significantly with increasing temperature.
• Contact time: The longer the contact time, the greater the migration amount. PS6 material begins to release long-chain alkanes after 10 minutes of contact with 100°C boiling water, and the migration amount continues to increase with time.
• Food type: Fatty foods accelerate plasticizer migration. The leaching rate of PAEs in different food simulants is ranked as follows: isooctane > 10% ethanol > 4% acetic acid > water. Therefore, when using plastic containers for fried foods, spicy hot pot, and other high-fat foods, the amount of plasticizer dissolved increases significantly.
• pH value: Acidic foods accelerate dissolution. For example, when a PET bottle contains 4% acetic acid, the migration amount of the harmful substance antimony is far higher than when it contains 10% ethanol or 20% ethanol. Acidic substances such as vinegar promote the release of trace substances from the material.

3. Short-Term Use Safety Assessment

3.1 Definition and Scenario Analysis of Short-Term Use

• Immediate consumption scenario: Hot soup is consumed within 15 minutes of being poured into a microwave-safe plastic bowl, with the soup temperature rapidly dropping from 70-100℃ to 60-70℃.
• Short-term storage scenario: The soup is consumed after being left for 15-30 minutes, with the temperature dropping to 50-60℃.
• Takeaway delivery scenario: The most common short-term scenario, delivery time often exceeds 30 minutes, the soup temperature drops sharply by more than 10℃, and the temperature drop reaches 20-30% after 15 minutes of delivery.

3.2 Safety Assessment of PP Material Round Plastic Bowls

• Advantages: PP material is a relatively safe choice for short-term use, with a heat resistance of 100-140℃, suitable for most hot soup temperatures; it has strong chemical stability, no harmful substances are released under normal and high temperatures, and there is no change in dissolved residue during high-temperature immersion experiments; the microplastic release amount (12,000 particles/cm²) is far lower than that of PS material.
• Potential risks: When in contact with high-temperature oily foods, it will accelerate the migration of additives, oligomers, and other harmful substances (such as phthalates); long-term frequent use, even if the single migration amount meets the standard, still poses an accumulation risk.

3.3 Safety Assessment of PS Material Round Plastic Bowls

• Core risks: Poor heat resistance (upper limit 75℃), softens at 75℃ and releases styrene monomer (a Class 2B carcinogen) at 80℃; the microplastic release amount is nearly 3 times that of PP material, highlighting safety issues.
• Usage restrictions: The temperature should not exceed 65℃. Even short-term contact with overheated hot soup will release harmful substances that endanger health. It can only be used for cold drinks, cold dishes, and room-temperature food, and is strictly prohibited from contact with hot soup or hot oil.

3.4 Safety Assessment of Other Material Round Plastic Bowls

• PET material: Heat resistance is only 60-70℃, it deforms at higher temperatures and releases acetaldehyde, which can irritate the digestive tract mucosa with long-term ingestion, making it completely unsuitable for hot food. PVC Material: Highest risk, releases chlorides and phthalates at high temperatures. Experiments show that PVC food containers holding eggplant stew at 60°C for 30 minutes resulted in plasticizer migration exceeding national standards by 11 times. Strictly prohibited for food contact.
• Composite Materials: Some lunchboxes use PP for the container body and PS (transparent and hard) for the lid, posing safety risks. The lid must be removed during heating to prevent PS from contacting high temperatures.

3.5 Comprehensive Safety Evaluation

 

4. Health Risks and Safe Use Recommendations

4.1 Main Harmful Substances and Health Effects

• Phthalates (plasticizers): In commercially available disposable plastic food containers, DEP and DIBP were detected in 100% of samples, and DBP and DEHP were detected in 78% of samples.
• Health effects include: endocrine disruption (estrogen-like effects, affecting male sperm production and increasing the risk of breast disease in women); developmental toxicity (precocious puberty in children, abnormal male reproductive organs, obesity, and increased risk of attention deficit hyperactivity disorder); and increased cardiovascular risk (activating oxidative stress and inflammatory pathways, interfering with lipid metabolism and blood pressure regulation, leading to elevated triglycerides and decreased high-density lipoprotein cholesterol).
• Styrene monomer: Released from PS material at high temperatures, a Class 2B carcinogen. Short-term exposure to large amounts irritates the respiratory tract and causes dizziness and nausea; long-term low-dose intake damages the liver and disrupts the endocrine system.
• Bisphenol A (BPA): Although strictly restricted by new regulations, it may still be present in some materials. It has endocrine-disrupting effects, affecting reproductive development, thyroid function, and metabolic regulation. At 80°C, the release amount soars to 1.2 μg/L, and long-term intake is harmful to health.
• Microplastics and nanoplastics: Preliminary studies show that they can cause digestive system damage (glucose intolerance, liver damage, and increased intestinal permeability in mice), increase cardiovascular risk (penetrating the intestinal barrier to form vascular inflammatory foci, with those detected having a 4.53 times higher risk of heart disease, stroke, or all-cause mortality), and affect the nervous system (carried by immune cells to cerebral blood vessels, leading to vascular blockage, cerebral thrombosis, and neurobehavioral abnormalities).

4.2 Risk Assessment for Special Populations

• Children: Their immune and endocrine systems are not fully developed. Phthalates can cause precocious puberty and reproductive abnormalities, and microplastics can quickly penetrate the intestinal wall of children and be detected in the blood within 48 hours.
• Pregnant women: Harmful substances (such as plasticizers) can cross the placental barrier and affect the fetus, causing malformations, nervous system damage, or low birth weight.
• Elderly people: Decreased liver and kidney function weakens their ability to metabolize harmful substances, and long-term exposure increases the burden on the liver and kidneys.
• Immunocompromised individuals: Patients with underlying diseases and those receiving immunosuppressive treatment have low tolerance to harmful substances and are prone to health problems.

4.3 Safety Usage Guidelines

• Material Selection: Prioritize PP5 material (look for the number "5" label, the only disposable tableware suitable for microwave use); avoid PS6 material (not suitable for food above 60°C); and reject PET1 and PVC3 materials (PET is only for cold drinks, and PVC is strictly prohibited from contact with food).
• Temperature Control: Use a food thermometer to measure the soup temperature to ensure it does not exceed the material's heat resistance; cool freshly cooked hot soup in another container to below 70°C before pouring it into the plastic bowl.
• Time Control: Minimize the time hot soup is stored in the plastic bowl; ideally, consume it within 15 minutes.
• Usage Precautions: Avoid using the round plastic bowls for high-temperature, high-oil foods such as spicy hot pot or hot and sour soup. If unavoidable, remove the surface oil first (reducing the migration of 42% of lipid-soluble harmful substances); after receiving takeout, quickly transfer the food to a ceramic or glass bowl; strictly prohibit microwaving plastic food containers; check the container for cracks, damage, or deformation before use, and replace it if any abnormalities are found.

 

5. Summary and Recommendations

5.1 Safety Summary

• PP material is relatively safe but has limitations: PP5 material is the only relatively safe plastic black bowls, with a heat resistance of 100-140°C. When used for hot soup below 70°C for short periods (15-30 minutes), the migration of harmful substances meets standards, but contact with high-temperature oil still accelerates migration, and frequent long-term use carries cumulative risks.
• Other materials pose high risks: PS6 material has a heat resistance of ≤75°C, releasing carcinogens at high temperatures, and is prohibited for hot soup; PET1 and PVC3 materials are even less safe and are strictly prohibited for hot food.
• Temperature is a key risk factor: 65°C is the safety threshold for polystyrene food containers, and 70°C is the risk temperature for most plastics, while freshly cooked hot soup (70-100°C) far exceeds the safe range, posing significant risks.
• Microplastic pollution cannot be ignored: Even PP material releases microplastics at high temperatures, and the long-term effects of ingestion require further research. 5.2 Daily Use Recommendations
• Based on safety assessments, daily use recommendations are categorized into three levels:
• Strongly Recommended (Safest): Use 304 stainless steel, high borosilicate glass, or ceramic tableware; choose environmentally friendly disposable tableware made from materials like sugarcane pulp; allow hot soup to cool to below 60℃ before using PP5 material round plastic bowls.
• Use When Possible (Moderately Safe): Use PP5 material round plastic bowls for hot soup below 70℃ for no more than 15 minutes; avoid high-fat foods, or remove excess oil before use; transfer takeout food immediately to safe containers.
• Avoid Using (High Risk): Do not use PS6, PET1, or PVC3 materials for hot soup; do not use round plastic bowls of unknown material or without markings; strictly avoid microwave heating or long-term storage of hot soup in these containers.