What specific chemical compounds commonly found in sunscreens are known to be toxic or damaging to coral reefs, and what are the mechanisms by which they cause harm (e.g., interfering with reproduction, causing bleaching, disrupting endocrine systems)? Also, are there any concentrations at which these chemicals are considered safe, and what non-chemical or alternative sunscreen ingredients are considered reef-safe and effective in protecting human skin from UV radiation?

Answer

Certain chemical sunscreen ingredients have been identified as harmful to coral reefs. The primary culprits are:

• Oxybenzone (Benzophenone-3): This UV filter is highly effective at absorbing UVB and short-wave UVA rays. However, it has been shown to cause:

  • Coral bleaching: Even at extremely low concentrations (parts per trillion), oxybenzone can disrupt the coral’s endocrine system, leading to the expulsion of algae (zooxanthellae) that provide the coral with food and color. This causes the coral to turn white and become more susceptible to disease and death.
  • DNA damage: Oxybenzone can damage the DNA of coral larvae, hindering their development and reproduction.
  • Deformities: It can cause deformities in coral larvae, making it difficult for them to settle and grow into healthy adult corals.
  • Endocrine disruption: As mentioned earlier, oxybenzone can interfere with the hormonal balance of corals, affecting their reproduction and growth.

• Octinoxate (Octyl methoxycinnamate): Another common UV filter that absorbs UVB rays. Its harmful effects include:

  • Coral bleaching: Similar to oxybenzone, octinoxate can induce coral bleaching.
  • DNA damage: It can also damage coral DNA and impair coral reproduction.
  • Endocrine disruption: Octinoxate has the potential to disrupt the endocrine system of marine organisms, including corals.

• Octocrylene: This UV filter is used to absorb UVB and UVA rays and is also used as a stabilizer for other UV filters. Studies have indicated that it accumulates in coral tissues and can:

  • Disrupt endocrine function: This can affect the coral’s reproduction and growth.
  • Cause coral bleaching: It can contribute to coral bleaching, particularly in combination with other pollutants.
  • Cause deformities: Can contribute to coral larvae deformities.

• Homosalate: A UV filter that absorbs UVB rays and is used to help other sunscreen ingredients penetrate the skin. It is suspected of:

  • Endocrine disruption: Similar to oxybenzone and octinoxate, it may disrupt the endocrine system of marine organisms.
  • Impacting neurological systems: Evidence suggests it can have a negative impact on the nervous system of marine life.

• Avobenzone: While avobenzone itself isn’t directly implicated as harmful to coral reefs, it’s often stabilized by other chemicals like octocrylene, which, as mentioned above, has been found to be harmful.

• Nanoparticles of Zinc Oxide and Titanium Dioxide: While mineral sunscreens containing zinc oxide and titanium dioxide are generally considered safer for coral reefs than chemical sunscreens, some studies have raised concerns about the use of nanoparticles (very small particles) of these minerals. Nanoparticles can:
  • Be ingested by corals: Due to their size, they can be ingested by corals and other marine organisms.
  • Cause oxidative stress: They may generate reactive oxygen species, leading to oxidative stress and cellular damage in corals.
  • However, it’s important to note that non-nano zinc oxide and titanium dioxide are considered reef-safe alternatives.

Other ingredients that may pose a threat:

• Parabens: These preservatives, such as methylparaben and butylparaben, can disrupt the endocrine system of marine organisms.
• Triclosan: An antibacterial agent that can accumulate in coral tissues and disrupt their hormonal balance.
• Microplastics: Some sunscreens may contain microplastics, which can pollute the marine environment and be ingested by marine organisms.

It is important to note that the effects of these chemicals on coral reefs are complex and can vary depending on factors such as concentration, exposure time, and the health of the coral reef ecosystem. Further research is needed to fully understand the impacts of these chemicals and other pollutants on coral reefs.