Monday, March 19, 2007

Is Eating Seaweed Dangerous?

I was wondering if you could tell me how safe eating seaweed is these days, pollution wise. I hear lots about fish, but nothing about seaweed. Our family consumes 6-12 ounces a week. We buy organic, but it's wild caught. I eat seaweed in salads, sandwiches, and sushi. Mostly we just snack on dulse. -which I believe comes from the Atlantic. And we use Kombu, kelp, when cooking soups and beans. I believe the Kombu is local. We're in Santa Cruz, Ca. Thanks so much for your time!

Edible seaweed is a marine algae that can come in many forms, including the type that you mention kombu, as well as the commonly eaten wakame and nori seaweeds. Although long part of the Asian diet, edible seaweed has increasingly become a part of Western diets due to its well-documented nutritional and often discussed medicinal qualities.

In comparison, there is little information about the possible negative effects of eating seaweed. A couple of years ago, several governments, including the Canadian and British governments, issued warnings advising people not to eat one type of seaweed – hijiki – because of concern over high levels of inorganic arsenic, a toxic element that has been linked to cancer, that was found in seaweed samples. Since little was known about the specific risks of arsenic in hijiki, hijiki was not banned. The warnings, which were intended to give the consumers a choice, explicitly stated that eating hijiki occasionally was probably not dangerous. Importantly, the warnings did not apply to other more commonly eaten seaweeds, including arame, nori, kombu, and wakame, which were found to be free of arsenic.

Based on these and other concerns, several scientific studies have been performed to measure the amount of metals present in seaweed. Results from these studies show that metal contamination of seaweed depends on three major factors, including where the seaweed was harvested, the type of seaweed, and the specific metal. For example, in a small Canadian study (Van Netten et al., Science of the Total Environment, 2000), seaweed grown in waters near British Columbia, Canada generally had lower amounts of heavy metals, especially of mercury, than seaweeds grown in Japan and Norway, possibly due to lower amounts of these metals in British Columbia waters. All seaweed samples – even those grown in Japan and Norway – however, had metal levels that are generally thought of as safe to eat.

What this means for you and your family is that you can continue to enjoy your seaweed salads, soups, and sushi (although given the governmental warnings I would probably stay away from hijiki). Given seaweed’s many nutritional benefits and relatively low pollutant levels, seaweed is probably not only a safe food but also one that is good for your health.

What is Vapor Intrusion? Should I Care?

Could you discuss the issues and health risks related to "vapor intrusion" of volatile organic chemicals into buildings from contaminated sites? What can a homeowner or purchaser do to find out if there is a vapor intrusion risk at home, schools, or day care centers?

“Vapor intrusion” (sometimes called “soil gas vapor intrusion”) is what happens when chemicals move from the ground or water into your home or other buildings. Chemicals that enter your home through the ground often belong to a class of chemicals called “volatile organic compounds” (VOCs), which as their name implies are volatile, and thus like to exist as a gas.

This property is important, allowing VOCs to move easily through openings that exist between the soil grains and thus to move from areas of high pressure to areas of low pressure. Since basements tend to be at lower pressure than the ground below, this pressure-related movement can cause VOCs to enter your home from the ground through openings or cracks in your foundation. Once inside, the VOCs can spread through out your home with the help of natural air flow, room or house fans, or other home ventilation devices. When this occurs, vapor intrusion can be an important source of indoor pollution in your home.

Whether vapor intrusion also presents additional health risks depends on many factors. For example, health risks will depend on the people that live or spend time in your home, as people have different responses to chemical exposures. Health risks will also depend on the type and amount of your chemical exposures, more precisely the specific VOCs that enter your home, their levels inside your home, and the length of time that the VOCs remain elevated.

Although other kinds of chemical spills, leaks or contamination can also lead to vapor intrusion in homes, the most common VOCs associated with vapor intrusion are gasoline-related, the result of spills or leaks from an underground storage tank at a gas station. For gasoline-related intrusions, VOCs of concern may include (but are certainly not limited to) benzene, toluene, xylenes, and styrenes. Exposures to these and other gasoline-relaed VOCs have been linked to a variety of adverse effects, including short term (and generally reversible) effects such as eye and respiratory irritation, headaches, and nausea, and long-term effects, such as cancer.

There are several ways to test if VOCs or other chemicals are entering your home through the ground. You can collect samples in the nearby ground (soil vapor samples), in the ground directly below your foundation (sub-slab vapor samples), in your indoor air, and in your outdoor air (for comparison). Samples in these different places should be collected at the same time, preferably during the heating season when the pressure difference between the ground and the basement should be highest. Similarly, indoor samples should be collected in the basement or first floor of the living space, since these are the areas in your home where the levels from vapor intrusions should be highest. Since there are many sources of VOCs inside your home and since indoor VOC concentrations can vary widely day-to-day, indoor sampling results may be more difficult to interpret than the soil and sub-slab sampling results, but interpretation of indoor sampling results will be easier with outdoor sampling data and information about your house, including its ventilation, characteristics, and other VOC sources.

Also, if you know that a nearby gas station, commercial or industrial facility or other site has had a spill or a leak of VOCs, you may want to call the owners, local government officials, or the people cleaning up the spill to see if any sampling is being performed to test for vapor intrusion and if so, to ask for testing to be performed at your home. The U.S. Environmental Protection Agency provides extensive technical guidance on vapor intrusion including “safe” levels of chemicals in groundwater and soil gas (See Draft Guidance at

If tests show that chemicals are getting into your home through the ground, there are many possible solutions, including sealing cracks and openings in the foundation or installing a radon remediation system. Often, the costs of these solutions will be paid for by the person or company who allowed the chemicals to get into the ground.

Wednesday, March 7, 2007

Pollution from Paraffin Heaters: Is It a Problem?

I have a passive solar house that gets most of its winter heat from the sun. I have a backup woodburning masonry stove that provides heat to my living room, kitchen, dining room open space. But my bedrooms do not yet have backup heating from a renewable heating source. So for the meantime I use a small portable paraffin heater in my master bedroom-bathroom. In the cloudiest two months of the cold season (basically the rainy months) I have to use this heater most evenings for at least a few hours. I usually turn it off at midnight or so. Some days I have to leave it on all day (but not during the night). My house is fairly well ventilated. My wife and I wonder what kind of pollutants these heaters give off and how much we have to worry about it. Could you give me some advice? Thank you.

Portable paraffin (often called kerosene) heaters have been used for a long time to heat indoor spaces. Paraffin heaters produce heat by burning fuel (in this case paraffin or kerosene). Since they do not require electricity, many people find them to be an attractive supplemental heating method.

Paraffin heaters generally follow a similar design, including a fuel tank, a wick to draw kerosene from the tank to the combustion area, a device to ignite the wick, and an automatic device that puts out the wick if the heater is accidentally turned over. Most newer heaters also have additional safety features to reduce the risks that would come from improper use or maintenance.

Despite these safety precautions, paraffin heaters pose a fairly significant fire hazard. This risk of fire is greatest if gasoline instead of paraffin is used as the fuel source and if the paraffin heater is not properly maintained or operated. Many governmental agencies and fire departments believe that the risk of fire from paraffin heaters is greater than that for other portable heating devices.

Paraffin heaters also pose a risk to health. Paraffin heaters, especially those that are unvented to the outside (as would the case be with a portable heater), are a significant source of indoor air pollution Research studies, including those conducted by my colleagues, have shown that paraffin heaters emit a number of pollutants typically associated with combustion or burning, including carbon monoxide, nitrogen oxides and sulfur dioxide, as well as polycyclic aromatic hydrocarbons and phthalates, among other pollutants. Exposures to these pollutants have been linked to a variety of adverse effects, ranging from headaches to breathing difficulties to death. These effects may occur shortly after breathing in these pollutants or may occur after years of exposure. They may also occur more readily in certain susceptible people, such as the elderly, children, and people with asthma.

Your exact health risks will depend on your susceptibility and also on your exposures to the heater-associated pollutants. Your home being fairly well ventilated is in your favor, as the emissions from your paraffin heater will likely have less time to accumulate inside your room, and as a result, your room levels of -- and thus your exposures to -- heater-associated pollutants will be lower. This is why many paraffin heater manufacturers recommend that the heater only be used when a window or a door to another room is opened at the same time. One rule of thumb is to provide 1 square inch of window opening for each 1,000 BTUs of the heater rating. For example, if you have a 10,000 BTU heater, you should open an outside window 10 square inches to provide the necessary ventilation. If your home is an energy efficient home, you may need to ventilate your room even more.

Even with these and other safety precautions, I believe that the fire and health risks outweigh the convenience or other reasons for having a paraffin heater. If possible, I would recommend switching to a heater that is vented to the outside or switching to a different type of portable heater. Regardless, I would make sure to have several carbon monoxide monitors located in your bedroom and in other places in your home.