Understanding Polycyclic Aromatic Hydrocarbons (PAHs) in the Food Chain

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds consisting of two or more fused aromatic rings, formed primarily through incomplete combustion of organic matter. These persistent environmental pollutants enter the food supply via sources like vehicle exhaust deposition on crops, industrial processing, and especially high-temperature cooking methods such as grilling, smoking, and frying. In urban settings like Singapore, where street food culture thrives with barbecued satay and stir-fried seafood, dietary exposure becomes particularly relevant.

PAHs are classified by the International Agency for Research on Cancer (IARC) with several, like benzo[a]pyrene, labeled as Group 1 carcinogens due to their genotoxic properties, capable of causing DNA damage and mutations leading to cancer. Beyond cancer, chronic exposure links to cardiovascular disease, reproductive issues, and immune suppression. The recent study published in Scientific Reports utilized data from Singapore's Total Diet Study (TDS) to quantify these risks precisely for the local population.

Singapore Total Diet Study: Design and Execution

The Singapore Total Diet Study (TDS), conducted from 2021 to 2023 by the Singapore Food Agency (SFA) in collaboration with academic partners, represents a landmark effort to map chemical hazards in everyday diets. Unlike traditional monitoring that tests raw ingredients, TDS analyzes foods as consumed—prepared, cooked, and pooled—to reflect real-world exposure. A nationally representative food consumption survey of over 2,000 residents aged 15 and above used 24-hour recalls, capturing the multicultural diet of Chinese, Malay, Indian, and other communities.

281 core foods across 22 categories—from beverages and grains to sauces and composite dishes like laksa—were purchased as 4,215 sub-samples from supermarkets and markets. These underwent household-style preparation: washing, cutting, and cooking via methods like stir-frying, steaming, or boiling, informed by culinary experts from Temasek Polytechnic. Pooled into 494 analytical samples, they were tested at SFA's ISO-accredited National Centre for Food Science for contaminants including heavy metals, PFAS, mycotoxins, and PAHs (specifically PAH4: benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[a]pyrene).

Key Findings on PAH Concentrations in Singapore Foods

Analysis revealed elevated PAH levels in specific categories: nuts and seeds (e.g., peanuts, sesame), sauces and condiments (soy, oyster), fruiting vegetables (chilies, tomatoes), and fungi/seaweed. Fish and seafood showed variability, with stir-fried prawns or fish exhibiting higher PAHs than steamed versions, highlighting cooking's role. Mean concentrations remained low overall, comparable to regional peers.

• Nuts and seeds: Highest due to roasting/oil frying.
• Sauces: From caramelization in production.
• Fruiting vegetables: Environmental deposition amplified by stir-frying.
• Fungi/seaweed: Marine pollution uptake.

These insights pinpoint hotspots in Singapore's diet, where seafood consumption averages 200g weekly per capita, often wok-tossed in hawker centers.

Cooking Methods and Their Influence on PAH Generation

Cooking profoundly affects PAH formation via pyrolysis at temperatures above 300°C. Stir-frying, prevalent in Singaporean cuisine for dishes like sambal belacan or Hokkien mee, generates more PAHs than gentler steaming or boiling due to oil smoke and drippings. The TDS tested multiple methods per food, finding stir-fried fish slices with up to 2-3 times higher PAH4 than boiled equivalents.

SFA advises minimizing direct flame contact, using covered grills, and opting for lower-heat methods. For example, marinating meats with antioxidants like ginger or turmeric—common in local recipes—can reduce PAH by 40-60%. This culturally attuned advice empowers consumers while informing industry standards.

Probabilistic Dietary Exposure Modeling

To estimate exposure, researchers employed Monte Carlo simulation, a probabilistic method accounting for variability in consumption and contamination. Using TDS concentration data and consumption surveys, optimistic (lower-bound) and pessimistic (upper-bound) scenarios modeled daily intake for PAHs. Inputs included left-censored data handled via substitution (LOD/2 for <LOD), body weights by age/gender, and 10,000 iterations for robust distributions.

Results showed mean exposures well below health-based guidance values (HBGV), with nuts/sauces as top contributors (20-30% each). Children under 6 faced slightly higher relative exposures due to higher intake per kg body weight, but margins of exposure (MOE) indicated low concern.

Photo by adison clark on Unsplash

Health Risk Quantification: Lifetime Cancer Risk and DALYs

Employing WHO/IPCS potency factors, lifetime cancer risk (ILCR) from total PAHs ranged 4.63 × 10^-5 (optimistic) to 5.17 × 10^-3 (pessimistic), straddling the 10^-5 to 10^-4 tolerable benchmark. Population-attributable Disability-Adjusted Life Years (DALYs)—combining years of life lost and disability—totaled 0.236 to 92.5 years for Singapore's 6 million residents, a negligible fraction of overall disease burden (e.g., vs. 500,000+ DALYs from diet-related NCDs).

This low burden underscores effective regulation, yet vulnerable groups like frequent grill-food consumers warrant targeted education. For context, smoking contributes 10^-3 orders higher risk.

Singapore Universities' Pivotal Role in the Research

Academic expertise elevated this TDS from surveillance to science. Lead author Angela Li and colleagues from NUS Faculty of Science, Department of Food Science & Technology, provided analytical validation and exposure modeling. Kyaw Thu Aung holds joint appointments at SFA, NUS, and NTU School of Biological Sciences, bridging lab-to-policy. Wei Jie Seow from NUS Saw Swee Hock School of Public Health contributed epidemiological insights, while Duke-NUS informed pediatric risks.

NUS's state-of-the-art labs and NTU's biotech prowess exemplify Singapore's higher ed investment in food security, training PhDs who staff SFA and industry. Aspiring experts can pursue faculty roles or Singapore university jobs in this field.

Global Comparisons and Singapore's Standing

Singapore's PAH exposures align with or undercut peers: Australia TDS reports similar cereal/grill contributions; EU studies show higher smoked fish intakes elevating risk; Catalonia's matches closely at 10-50 ng/kg bw/day BaP equivalents. Unlike high-seafood Japan (higher marine PAHs), Singapore's regulated imports keep levels low.

• EU: Higher in oils/smoked products.
• Australia: Comparable nuts/veggies.
• China: Elevated urban grilling.
• Singapore: Lowest DALYs, effective mitigation.

This positions Singapore as a model for urban TDS in Asia.

Public Health Strategies and Mitigation Tips

SFA integrates TDS into risk prioritization, setting import alerts for high-PAH goods and educating via campaigns. Consumers reduce exposure by:

• Choosing steaming/boiling over frying.
• Trimming charred parts.
• Ventilating kitchens.
• Diversifying diets beyond nuts/sauces.

Industry adopts clean-label processing; e.g., post-TDS, some sauces reformulated. For higher ed, this fuels curricula in food tech at NUS/NTU, fostering innovation like PAH-degrading enzymes.SFA cooking tips

Future Outlook: Expanding Research Horizons

Building on TDS, NUS/NTU plan longitudinal biomonitoring and climate-PAH links, amid RIE2030's S$37B science push. Emerging focus: microplastics-PAH synergies, AI predictive modeling. Singapore's universities lead, attracting global talent—check academic CV tips for entry.

Photo by Natália Catunda on Unsplash

Career Pathways in Food Safety and Public Health Research

This study spotlights booming demand for food scientists. NUS/NTU grads secure roles at SFA, startups, or research assistant positions. Rate professors via Rate My Professor, explore higher ed jobs, or career advice. With Singapore's food import reliance (90%), expertise is vital.

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