WHO's Q&A on Red Meat and Processed Meat

Lyon, France, 26 October 2015 – The International Agency for Research on Cancer (IARC), the cancer agency of the World Health Organization, has evaluated the carcinogenicity of the consumption of red meat and processed meat.

• Processed meat was classified as carcinogenic to humans (Group 1), based on sufficient evidence in humans that the consumption of processed meat causes colorectal cancer.
• Red meat as probably carcinogenic to humans (Group 2A), based on limited evidence that the consumption of red meat causes cancer in humans and strong mechanistic evidence supporting a carcinogenic effect.

What the TV medias did not tell you clearly about the hazard and risk of eating red meat and processed meat:

Hazard vs Risk

IARC classifies carcinogens in five categories ranging from carcinogenic to humans (Group 1) to probably not carcinogenic to humans (Group 4). 

• Group 1: The agent is carcinogenic to humans
• Group 2A: The agent is probably carcinogenic to humans (convincing evidence that the agent causes cancer in laboratory animals and some evidence that it could cause cancer in humans, but the evidence in humans is not conclusive)
• Group 2B: The agent is possibly carcinogenic to humans (convincing evidence that the agent causes cancer in experimental animals but little or no information about whether it causes cancer in humans)
• Group 3: The agent is not classified as to its carcinogenicity to humans
• Group 4: The agent is probably not carcinogenic to humans

However, the classification indicates the weight of the evidence as to whether an agent is capable of causing cancer (technically called “hazard”), but it does not measure the likelihood that cancer will occur (technically called “risk”) as a result of exposure to the agent. The IARC Monographs Programme may identify cancer hazards even when risks are very low with known patterns of use or exposure.

The Groups indicate the strength of the evidence regarding a cancer hazard and not the risk, the risk associated with two agents classified in the same Group may be very different. Comparisons within a category can be misleading:

1. Exposures may vary widely. For example, there is widespread exposure to the Group 1 agent air pollution, whereas far fewer people would be exposed to certain Group 1 chemicals, such as 1,2-dichloropropane. 
2. The magnitude of risk associated with exposure to two agents may be very different. Active smoking carries a much higher risk of lung cancer than does air pollution, although both are categorized in Group 1. 
3. The number of resulting cancers can be different; for example, tobacco smoking causes some common cancers, whereas 1,2- dichloropropane causes a rare bile duct cancer. This also applies to Group 2 agents. For example, radiofrequency electromagnetic fields and the prescription drug digoxin are each classified in Group 2B.

What types of cancers are linked with eating red meat and processed meat

• Processed meat - Colorectal cancer. An association with stomach cancer was also seen, but the evidence is not conclusive. An analysis of data from 10 studies estimated that every 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%. There is also not enough information to say whether higher or lower cancer risks are related to eating any particular type of processed meat or red meat. 
• Red meat - Colorectal cancer. There is also evidence of links with pancreatic cancer and prostate cancer. If the association of red meat and colorectal cancer were proven to be causal, data from the same studies suggest that the risk of colorectal cancer could increase by 17% for every 100 gram portion of red meat eaten daily. How much meat is it safe to eat? The risk increases with the amount of meat consumed but the data available for evaluation did not permit a conclusion about whether a safe level exist. 
• The cancer risks associated with consumption of poultry and fish were not evaluated.

What makes red meat and processed meat increase the risk of cancer

Meat consists of multiple components, such as haem iron. Meat can also contain chemicals that form during meat processing or cooking. For instance, 

• Carcinogenic chemicals that form during meat processing include N-nitroso compounds and polycyclic aromatic hydrocarbons. 
• Cooking at high temperatures or with the food in direct contact with a flame or a hot surface, as in barbecuing or pan-frying, produces heterocyclic aromatic amines as well as other chemicals including polycyclic aromatic hydrocarbons, which are also found in other foods and in air pollution. Some of these chemicals are known or suspected carcinogens, but despite this knowledge it is not yet fully understood how cancer risk is increased by red meat or processed meat.

Ref: http://www.who.int/features/qa/cancer-red-meat/en/

Supermoon 2015

Nikon D700  1600mm
Mid-Autumn Festival @Hong Kong 2015

From Vacuum Pump to Flush Toilet

I learned vacuum pumps 28 years ago in the Material Science course. At atmospheric pressure and mild vacuums, molecules interact with each other and push on their neighbouring molecules in what is known as viscous flow. For UHV (Ultra-High Vacuum) applications, about 10⁻⁷ pascal (10⁻⁹ mbar, ~10⁻⁹ torr), requires multiple vacuum pumps in series and/or parallel working together. Categorised by technologies, there are broadly three types of pumps:

1. PULL/拉 Displacement pumps for low vacuums (e.g. piston pump), 
2. PUSH/推 Momentum transfer pumps in conjunction with one or two positive displacement pumps to achieve high vacuums, 
3. Entrapment pumps used in the final stage to reach ultrahigh vacuums.

In daily life, we move unwanted thing away by push and pull. When we do it, momentum of the object change. In a momentum transfer pump, gas molecules are accelerated from the vacuum side to the exhaust side. But the pumping action is only possible below pressures of about 0.1 kPa or 1 mbar (1 bar ~= atmospheric pressure on Earth at sea level). This regime is generally called high vacuum (because the distance between the molecules increases, the molecules interact with the walls of the chamber more often than with the other molecules. So molecular pumping becomes more effective than displacement pumping).

The two main types of molecular pumps are the diffusion pump and the turbomolecular pump. Both types of pumps blow out gas molecules that diffuse into the pump by imparting momentum to the gas molecules. During the operation, a base pressure will be reached when leakage, outgassing, and back streaming equal the pump speed.

Turbomolecular Pump

Diffusion Pump

Flush Toilet

What can we tell if applying the knowledge of pumps to the flush toilet? First, both are on moving floating (air/water) things (dusts and particles/“things”) from one place to another place. Second, the chambers are very different. For the vacuum systems, pumps are mounted to the exhaust of the sealed close chambers. But for flush toilet, the chamber is the open bowl. Third, since there is no moving part, the flush toilet is similar to the diffusion pump system.

Consider the design of the flush toilet, “things” are flushed through the pipe by the water jet from the tank (conventional: 10L/flush, modern low flush toilet: ~5L/flush) with the help of siphon of the S-shaped trapway.

In fluid dynamics, Bernoulli's principle states that for an ideal fluid with no viscosity and heat flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. This is equivalent to, in a steady flow, the sum of all forms of energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy, potential energy and internal energy remains constant.

Apply Bernoulli’s equation to the siphon:

we can determine,

1. Velocity of the siphon v_c is driven solely by the height difference between the surface of the upper reservoir and the drain point. That means, the sucking force is directly proportional to the total weight of water inside the filled tube! 
2. Maximum height of the intermediate h_b high point occurs when it is so high that the pressure at the intermediate high point is zero; this will cause the liquid to form bubbles and if the bubbles enlarge to fill the pipe then the siphon will "break". The value is about 10m for water. 

What is the volume of water to start the siphon inside the bowl? The amount is small. You can see it from the video at below. Also note that the waterways in the siphon toilets are designed with slightly smaller diameters than a non-siphoning toilet, so that the waterway will naturally fill up with water, each time it is flushed, thus creating the siphon action.

Conclusion

1. You see a large flow of water running down the bowl carry away the “things”. But it is not the complete story, siphon of the S-shaped trapway (inverted “U”) is the main mechanism of sucking.
2. Running water from the tank acts like a diffusion pump. It is in serial connection with a displacement pump in which now is the siphon action.
3. Because the amount of water to start the siphon is small. So siphon happen quickly after the start of water flow. The following water running from the tank until stop is the current carrying the “things” along the pipe.
4. The followings will either “kill” or slow down the siphon at the beginning:

• blocked trapway, 
• pipe leakage (below normal water level), 
• frozen pipe (empty trapway), 
• back streaming (imbalance of water pressure).

Take Home Lessons

1. Make a clean flush before using the toilet (put down the cover may increase the downward force).
2. After using the toilet, before trigger the flush, gently pour some water into the bowl (may consider using hot water in winter).  
3. Uses toilet tissue not facial tissue. Toilet tissue is designed to decompose in septic tanks because its fibres is shorter. Compaction of toilet paper in drain lines, such as in a clog, prevents fibre dispersion and largely halts the breakdown process.
4. Don’t rush Wait a few seconds before trigger the flush may help softening the tissue in water.