White, brown or red?

For many people summer is synonymous of beach and tan. But there are people who are not tan during winter. Some people prefer to use UVA tanning booths a few months before, and others take the sun without protection to catch some colour. What consequences can this have? Then I will talk about the skin and the effect of radiation on it.

OUR SKIN

The skin is the largest organ of our body, has an area between 1.5 and 2m² of surface and a weight around 3.5-5kg. Their functions are:

• Protection: protects the internal organs from trauma and prevents the loss of water and electrolytes from the inside.
• Thermoregulation: the blood vessels increase or decrease the temperature of the skin. When it is very hot the sweat refreshes the skin surface.
• Sensitivity: the perception of touch, pressure, temperature, pain and itching is done through the skin.
• Secretion: the skin protects the body from dehydration.
• Excretion: through the skin we eliminate about 350ml per day of water, which we have to recover by moisturizing. In certain diseases you can get rid of a lot of protein and sulfur.

The skin has two basic cells: keratinocytes (80%) and melanocytes (10%). The melanin, which gives the tan, is found inside the melanocytes and accumulates in some bags (melanosomes). When it does not touch the light it remains in deep strata, whereas when it touches the sun goes up by the keratinocytes (Figure 1).

Figure 1. Melanin (arrows) rising towards the keratinocytes (Source: Salud del Siglo XXI)

Tan is the synthesis of new melanin. Not all people produce the same amount of melanin. We all have the same number of melanocytes, but the difference is in the number of melanosomes.

Our skin is formed by 3 layers that are, ordered from superior to inferior, epidermis, dermis and hypodermis (Figure 2).

Figure 2. Skin layers: A) epidermis, B) dermis and C) hypodermis (Source: MedlinePlus)

The tanning process passes into epidermis, which is the top layer of the skin. Epidermis is 0.2mm thick and subdivided into 4 or 5 layers, depending on the body part. For example, the palms of the hands and soles of the feet are formed by 5 layers, where the extra layer gives more resistance. The thickness of the skin in these areas is 1-2mm, in contrast, in other areas, as in the eyelids, is lower (0.004mm). In the inner or deep layers, the cells are younger and more active, and along the cycle, they ascend to the outer or superficial area, becoming dead cells, without nucli and formed basically by keratin (dead skin).

Below, there is dermis that gives elasticity to the skin, where you find the nerves and blood vessels and is where the hairs and nails grow. Finally, hypodermis is below everything and is where the glands are.

RADIATION FROM OUR SKIN

The sun emits radiation with wavelengths ranging from 0.1 to 17,000nm. But only the radiations between 280 and 3,000nm arrive to the Earth (the others remain in the ozone layer).

Radiation that affects living organisms involves spectrum of 280-800nm (UVB, UVA, visible light and a part of infrared) (Figure 3).

Figure 3. Electromagnetic spectrum (Source: J. E. Martin Cordero. Agentes Físicos Terapéuticos (2009))

Not all radiation penetrates in the same way on our skin. Table 1 shows the level of penetration:

Table 1. Penetration according to the different radiation.

Type		Wavelenght	Level of penetration
Ultraviolet	UVC	100-280nm	–
	UVB	280-315nm	Epidermis
	UVA	315-400nm	Dermis
Visible light	VL	400-700nm	Dermis
Infrared	IR	>700nm	Hypodermis

It is important to know that prolonged exposure, without taking precautions, can not only produce skin cancer, but can also have other effects. UVB radiation is the most common cause of sunburn, erythema or redness. It is also the most common cause of skin cancer. In contrast, UVA radiation rarely causes burns, but is responsible for most photosensitization (abnormal increase in skin sensitivity to UV radiation) and may be carcinogenic in the presence of certain substances that enhance its effect. In addition, it causes aging of the skin (Figure 4).

In tanning booths 30% of the radiation is UV. Mostly it is UVA radiation, but there is also UVB radiation (albeit to a lesser extent). The remaining percentage is infrared radiation and visible light.

Figure 4. UVA (aging) and UVB radiation (burns) effects (Source: Antirughe.info)

The amount of irradiation is greater when the more near is the Earth of the Sun (zone of the Equator, between the Tropics of Cancer and Capricorn, or between 12 and 16 hours). This irradiation can damage our DNA, causing breaks in the DNA strand that can cause mutations.

UV rays easily pass through clouds and water vapor, but are partially absorbed by atmospheric pollution. It has been seen that in areas where there are holes in the ozone layer the incidence of skin cancer is higher. This is because the damage caused in the ozone layer allows the passage of more amount of UVB rays. Here the importance of not damaging the ozone layer, as it protects us from these rays.

WE NEED TO PROTECT OUR SKIN

Since the light can be reflected by several substances, it is necessary to take into account that, to direct rays of the sun, can be added those that arrive tangentially on a bright day and that are reflected by sand, water, soil, gel, snow…

Radiation doses are cumulative and may add to the effects of ionizing radiation (X-rays). The presence of skin cancer can be observed many years after an acute burn. This has been observed in American sailors who were in the Pacific during World War II, and who were exposed for months or years to high intensity solar radiation. These sailors have developed over the years different types of skin cancer.

For this reason it is very important to take the correct sun protection measures: use photoprotectors, avoid long periods in the sun, especially in hours of maximum solar intensity; and moisturize often.

REFERENCES

• MedlinePlus
• Onmeda.es
• AEMET – Agencia Estatal de Metereología
• The Tech – Museum of Innovation
• American Cancer Society
• Canal Salut Gencat

The plants and the climate change

Since a few years ago, we have heard about the climate change. Nowadays, it is already evident and also a concern. This not only affects to us, the humans, but to all kind of life. It has been talked enough about the global warming, but perhaps, what happens to the vegetation has not been much diffused. There are many things affected by climate change and vegetation is also one of them. In addition, the changes in this also affect us. But, what are these changes? how can the vegetation regulate them? And how we can help to mitigate them through plants?

CHANGES ON PLANTS

Biomes distribution

In general, due to climate change, an increase of precipitations in some parts of the world are expected, while in others a decrease is awaited. A global temperature increment is also denoted. This leads to an alteration in the location of the biomes, large units of vegetation (e.g.: savannas, tropical forests, tundras, etc.).

Biome triangle classified by latitude, altitude and humidity (Author: Peter Halasaz).

On the other hand, there is an upward trend in the distribution of species in the high latitudes and a detriment in the lower latitudes. This has serious associated problems; the change in the species distribution affects their conservation and genetic diversity. Consequently, the marginal populations in lower latitudes, which have been considered very important for the long-term conservation of genetic diversity and due their evolutionary potential, are threatened by this diversity loss. And conversely, the populations in high latitudes would be affected by the arrival of other competing species that could displace those already present, being as invasive.

Species distribution

Within the scenario of climate change, species have some ability to adjust their distribution and to adapt to this.

But, what type of species may be responding more quickly to this change? It appears that those with a faster life cycle and a higher dispersion capacity will be showing more adaptability and a better response. This could lead to a loss of some plants with slower rates.

The Purple milk Thistle (Galactites tomentosa) is a plant with a fast life cycle and high distribution capacity  (Author: Ghislain118).

One factor that facilitates adjustment in the distribution is the presence of wildlife corridors: these are parts of the geographical area that enable connectivity and movement of species from one population to another. They are important because they prevent that some species can remain isolated and because they can also allow the movement to new regions.

Another factor is the altitudinal gradient, which provides shelter for many species, facilitates the presence of wildlife corridors and permits redistribution of species along altitude. Therefore, in those territories where there is greater altitudinal range, the conservation is favored.

In short, the ability of species to cope with climate change depends on the plant characteristics and the territory attributes. And, conversely, the species vulnerability to climate change occurs when the speed to displace their distribution or adapt their lives is less than the climate change velocity.

At internal level

Climate change also affects the plant as an organism, as it causes changes in their metabolism and phenology (periodic or seasonal rhythms of the plant).

One of the effects that pushes the climate change is the carbon dioxide (CO₂) concentration increase in the atmosphere. This could produce a fertilization phenomenon of vegetation. Due the CO₂ increase in the atmosphere it also increases the uptake by plants, thus increasing the photosynthesis and allowing greater assimilation. But, this is not all advantages, because for this an important water loss occurs due that the stomata (structures that allow gas exchange and transpiration) remain open long time to incorporate CO₂. So, there are opposing effects and fertilization will depend on the plant itself, but the local climate will also determine this process. Many studies have shown that various plants react differently to the CO₂ increase, since the compound affects various physiological processes and therefore there are not unique responses. Then, we find a factor that alters the plant metabolism and we cannot predict what will be the effects. Furthermore, this fertilizer effect is limited by the nutrients amount and without them production slows.

Photosynthesis process (Author: At09kg).

On the other hand, we must not forget that climate change also alters the weather and that this affects the vegetation growth and its phenology. This can have even an impact on a global scale; for example, could produce an imbalance in the production of cultivated plants for food.

PLANTS AS CLIMATE REGULATORS

Although one cannot speak of plants as regulators of global climate, it is clear that there is a relationship between climate and vegetation. However, this relationship is somewhat complicated because the vegetation has both effects of cooling and heating the weather.

The vegetation decreases the albedo; dark colours absorb more solar radiation and, in consequence, less sunlight is reflected outward. And besides, as the plants surface is usually rough, the absorption is increased. Consequently, if there is more vegetation, local temperature (transmitted heat) intensifies.

But, on the other hand, by increasing vegetation there is more evapotranspiration (set of water evaporation from a surface and transpiration through the plant). So, the heat is spent on passing the liquid water to gas, leading to a cooling effect. In addition, evapotranspiration also helps increase local rainfall.

Biophysical effects of different land uses and its consequences on the local climate. (From Jackson et al. 2008. Environmental Research Letters.3: article 0440066).

Therefore, it is an ambiguous process and in certain environments the cooling effect outweighs, while in others the heating effect has more relevance.

MITIGATION

Nowadays, there are several proposals to reduce climate change, but, in which way can the plants cooperate?

Plant communities can act as a sinks, carbon reservoirs, because through CO₂ assimilation, they help to offset carbon emissions. Proper management of agricultural and forest ecosystems can stimulate capture and storage of carbon. On the other hand, if deforestation were reduced and protection of natural habitats and forests increased, emissions would be diminished and this would stimulate the sink effect. Still, there is a risk that these carbon sinks may become emission sources; for example, due to fire.

Finally, we must introduce biofuels: these, unlike fossil fuels (e.g. petroleum), are renewable resources, since they are cultivated plants for use as fuels. Although they fail to remove CO₂ from the atmosphere or reduce carbon emissions, they get to avoid this increase in the atmosphere. For this reason, they may not become a strict mitigation measure, but they can keep neutral balance of uptake and release. The problem is that they can lead to side effects on social and environmental level, such as increased prices for other crops or stimulate deforestation to establish these biofuel crops, what should not happen.

Sugarcane crop (Saccharum officinarum) in Brazil to produce biofuel (Author: Mariordo).

REFERENCES

• Notes of Plant Physiology, Science of the Biosphere and Analysis of vegetation, Degree of Environmental Biology, UAB
• Hample & R. J. Petit. 2005. Conserving biodiversity under climate change: the rear edge matters. Ecology letters 8 (5): 461-467.
• Botanic Gardens Conservation International. 2015. How does climate change affect plants?. https://www.bgci.org/climate/climate_change_effects/
• Earth Observatory. 2015. How plants can change our climate. http://earthobservatory.nasa.gov/Features/LAI/LAI2.php