Overview, Common Classification and Human Health Hazards of Per- and Polyfluoroalkyl Substances (PFASs)
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1. Overview of Per- and Polyfluoroalkyl Substances (PFASs)
Per- and Polyfluoroalkyl Substances (PFASs) are a large group of man-made fluorinated organic compounds, widely recognized as "forever chemicals" due to their exceptional chemical stability. Characterized by strong carbon-fluorine bonds (C-F bonds) with high bond energy, PFASs are resistant to degradation in the environment and can accumulate persistently in both ecosystems and living organisms. These unique properties—including heat resistance, water repellency, oil repellency, and surface activity—have led to their extensive application in industrial production and daily consumer products. However, their environmental persistence and bioaccumulation potential have raised significant concerns regarding environmental pollution and human health risks.
2. Common Classification of PFASs
2.1 Classification by Carbon Chain Length (Most Widely Used)
- Short-chain PFASs: Refers to compounds with a carbon chain length of ≤ 6 carbon atoms (e.g., Perfluorohexanesulfonic acid, PFHxS). Some short-chain PFASs have been used as alternatives to long-chain ones, but they still pose potential environmental and health risks.
- Long-chain PFASs: Refers to compounds with a carbon chain length of ≥ 7 carbon atoms (e.g., Perfluorooctanesulfonic acid, PFOS; Perfluorooctanoic acid, PFOA). These were the most widely used PFASs in the past, with higher environmental accumulation and more significant toxicity concerns. Currently, most long-chain PFASs have been restricted or phased out in many regions due to strict regulatory requirements.
2.2 Classification by Functional Groups
- Perfluoroalkyl Sulfonates (PFSA): Representative substances include PFOS. They were historically used in detergents, fire-fighting foams, metal electroplating, and other industrial processes.
- Perfluoroalkyl Carboxylates (PFCA): Representative substances include PFOA. They were commonly used in non-stick cookware coatings, food packaging materials, and water/oil repellent treatment for textiles.
- Other Types: Including Perfluoroalkyl Phosphates (PAPs, used as surfactants), perfluoroethers (e.g., ether derivatives of PFBS, used in industrial cleaning agents), and more.
2.3 Classification by Application
- Industrial PFASs: Applied in fire-fighting foams (perfluoroalkyl surfactants), metalworking fluids, electronic component manufacturing, and other industrial fields.
- Consumer PFASs: Used in non-stick coatings, water- and stain-resistant fabrics, food contact materials, and cosmetics (e.g., waterproof lipsticks, mascaras).
3. Human Health Hazards of PFASs
PFASs' health hazards primarily stem from their "forever chemical" properties—slow metabolism and long-term accumulation in the human body—leading to potential adverse effects on multiple organs and systems. Many of these hazards have been confirmed by extensive scientific research.
3.1 Endocrine Disruption
PFASs can interfere with thyroid function, causing abnormalities in thyroid hormone levels. This disruption affects metabolism, growth, and development, with particularly higher risks for fetuses and infants.
3.2 Reproductive and Developmental Toxicity
Exposure to PFASs may reduce male sperm quality and quantity, and increase the risk of female infertility and miscarriage. Prenatal exposure can lead to low birth weight and developmental delay in fetuses.
3.3 Carcinogenic Risk
The International Agency for Research on Cancer (IARC) has classified Perfluorooctanoic acid (PFOA) as a Group 2B carcinogen (possibly carcinogenic to humans). Long-term exposure may increase the risk of kidney cancer, testicular cancer, thyroid cancer, and other malignancies.
3.4 Immune Function Impairment
PFASs can weaken the human immune system, making individuals more susceptible to infections. They may also reduce the effectiveness of vaccinations, especially in children.
3.5 Other Systemic Effects
Long-term exposure increases the risk of cardiovascular and metabolic diseases such as hyperlipidemia, hypertension, and diabetes. Additionally, some PFASs may cause liver damage and elevated cholesterol levels.
3.6 Key Characteristics of Hazards
- Strong Accumulation: PFASs are excreted slowly from the human body and accumulate persistently in blood, liver, and other tissues. The longer the exposure time, the higher the health risk.
- Low-Dose Effectiveness: Even low-concentration exposure to PFASs in the environment can have significant health impacts over the long term.
- Widespread Exposure Risk: PFASs enter the human body through multiple pathways, including drinking water, food packaging, non-stick cookware, and contaminated food, making complete avoidance difficult for the general population.