Fumigation is a means to control pests by enclosing a structure within a ‘tent’, injecting a gaseous pesticide and allowing the poison time to infiltrate nooks and crannies, thus killing targeted vermin. In Hawaii, using the pesticide Vikane™ (Dow AgroScience’s trade name for sulfuryl fluoride – F₂O₂S) is most often used to eliminate drywood termites. It is also used on the mainland to control other drywood termite species. Fortunately, drywood termites do not occur in all states and are restricted to warmer climates. But they can be a real problem in coastal North and South Carolina, south Georgia, Florida, south Alabama, coastal Mississippi, Louisiana, Texas, New Mexico, Arizona and southern California.

Licensed pest control specialists generally recommend removal of aquaria from the structure but might allow an aquarium to remain inside during treatment (using, of course, aeration from an air pump situated well away from and outside the building). They are doing what they are trained to do – recommend to the customer the best options for their pets. In fact, little is known about the effects of this pesticide on many animals. Indeed, Kollman (date unknown) states that effects of Vikane on fish, wildlife and other non-target organisms are not known.

Figure 1. “Tenting” a house for drywood termites. The tent contains the toxic gas within the structure.

Hawaii is a land of eternal summer where killing frosts don’t occur (unless you’re living on the peaks of the Big Island’s Mauna Loa, Mauna Kea or Maui’s Haleakala). Hence, invertebrates such as corals thrive, but less desirable inverts such as termites and wood-boring beetles also enjoy the sub-tropical climate, and these pests aren’t particular – they live in humble, ramshackle coffee shacks all the way up to multi-million dollar homes. While my home is decidedly somewhere-in-between, several termite colonies were quite content to dine on its wooden frame. Professional help was needed.

My fears were confirmed when the inspector recommended I remove 4 aquaria from the house. This would be a major project! I considered leaving the tanks in the house and simply supplying ‘clean’ air from outside, but rejected this notion. Instead, at almost the last minute, I decided to conduct a few experiments to determine the effects of the pesticide on a few selected invertebrates. Although this may sound cruel, I knew that moving the animals to an outside home and back again also involved risks to the health and lives of the captive animals. Perhaps something could be learned from this ordeal.

Figure 2. The experiment’s set up. Air temperature, water temperatures, photosynthetically active radiation (PAR) and pH were monitored.

The evening before the scheduled fumigation, I removed a few invertebrates from aquaria and randomly placed them in ten Mason jars containing 750 ml of aquarium water (see Figure 2). Five jars would be left uncovered and aerated from an air pump within the house. This would be the worst case scenario, where nothing was done to prevent the pesticide from making contact with the water and its inhabitants. Another five jars would be covered with two pieces cut from nylon polymer bags (NyloFume™, Dow AgroSiences) which are impermeable to Vikane. These were supplied by the exterminator to bag food, medicine and other goods from exposure. Aeration to these five containers was supplied by an air pump situated well away from the tented house.

Since the air conditioner would have to be turned off during fumigation, I had concerns about the temperature of the jars’ contents getting too high. I monitored air temperature and water temperature in one of the covered jars with a datalogger (WatchDog™ model 425, Spectrum Technologies) as well as light intensity (using a Spectrum PAR sensor modified for 60 Hz light). pH and temperature were monitored in an uncovered jar with a separate datalogger (Hach HQ40d™ multi-meter). Fluoride (as F^–) was measured using the SPADNS method and a Hach DR890 colorimeter (chloride concentrations exceeding 7,000 mg/l and sulfate exceeding 200 mg/l will cause high results, and distillation is recommended. This was not done, however it is assumed that there was no difference in the aliquots since they were originally from the same source. Hence the measurements should be valid for comparative purposes).

Figure 3. One of the Aiptasia anemones before fumigation with sulfuryl fluoride.

Results

None of the inhabitants of the covered jars suffered any apparent harm during fumigation. Results were different for some of the invertebrates exposed to the gas. Woven Topsnails (Trochus intextus) seemed particularly susceptible to the effects of fumigation and succumbed within 24 hours. Vikane was also deadly to Spiny Brittle Stars (Ophiocoma erinaceus), Ten-lined Sea Urchins (Eucidaris metularia), and Rock-boring Sea Urchins (Echinometra mathaei), but the effects were not immediate and the animals perished over the course of several days. Rock Anemones (Aiptasia pulchella) and an unidentified zoanthid (Protopalythoa sp.), were ‘burned’ during the fumigation event but survived (see Figures 3 and 4) and recovered in about 1 week. A green alga (Ulva) and unidentified red algae also survived exposure with no apparent harm or loss of photopigments.

Figure 4. The typical appearance of Aiptasia anemones after exposure to sulfuryl fluoride and chlorocipin. They appear to be ‘burned’.

Discussion

When examining the possible effects of sulfuryl fluoride on invertebrates, we must consider that another agent is also used during fumigation – chloropicrin. This is a warning agent (a ‘tear gas’) released in trace amounts into the structure to drive out people or animals the inspector might have missed (there’s a scary thought).

Sulfuryl fluoride is soluble in water (solubility = 750 ppm), and in alkaline water (including seawater) it undergoes rapid hydrolysis and forms fluorosulfuric acid (HSO₃ F) and fluoride. Hence we would expect to see a drop in pH when Vikane dissolved into the water – and this was noted in the open jar monitored for pH. See Figure 5.

Additionally, we would expect to see an increase in fluoride in the ‘exposed’ water. This, too, was noted – several days after fumigation, elevated fluoride was found in the water of the jars exposed to the fumigation gases. Natural seawater is used and the covered jars contained ~1 mg/l fluoride while the ‘exposed’ jars contained an average of 2.2 mg/l fluoride.

Air temperature and hence water temperatures stayed within an acceptable range during the experiment. See Figure 6.

Photosynthetically active radiation stayed at low values during the 12 hour photoperiod. Inadvertently, PAR records indicated exact times the tent was placed on and removed from the structure (the jars were situated near a window; data not shown).

Figure 5. Water pH fell sharply when chlorocipin and sulfuryl fluoride were released into the structure. The green line marks the beginning of fumigation, and the red line is when the ‘tent’ was removed and structure ventilation began.

Dissolved oxygen was not measured in the jars but aeration was probably sufficient. Further, decaying matter exerts an oxygen demand and none of the containers with mortalities generated any signs of anoxic or anaerobic activity (judged visually and by smell).

The results from this brief experiment suggest that temperature and pH modulations were not severe enough to cause distress or death in the affected animals. However, swings in these parameters correlated exactly with the release of the pesticide and its warning agent. Further, elevated fluoride levels found in the ‘open’ containers several days after exposure suggest sulfuryl fluoride did contribute to the demise of the marine invertebrates.

On a happier note, the specimens in the covered and aerated containers suffered no mortalities. This suggests that covering an aquarium with NyloFume™ bags and providing aeration from a source outside of the affected structure is sufficient to prevent contact with either the warning agent or pesticide.

Based on this evidence, I’ll elect to keep the aquaria inside the house and exercise all due precautions next time fumigation is needed. I lost a captive-bred Flame Angel due to stresses of moving him about (and not due to any effects of the pesticide). In retrospect, I should have simply covered the tanks and maintained good aeration and water circulation. If you find yourself in the same situation, where sulfuryl fluoride is the fumigant, perhaps you should consider this too. Discuss this with a licensed professional and reach an understanding first. My limited experiences suggest you and your aquarium will make it through just fine.

Figure 6

References

1. American Public Health Association, 1998. Standard Methods for the Examination of Water and Wastewater. Washington, DC.
2. Environmental Protection Agency, 2008. Structural fumigation using sulfuryl fluoride: DowElanco’s Vikane gas fumigant. http://www.epa.gov/ozone/mbr/casestudies/volume2/sulffury2.html
3. Hach Company, 1997. DR2010 Spectrometer Handbook. Loveland, Co.
4. Kollman, W., date unknown. Environmental fate of sulfuryl fluoride. Environmental Monitoring Branch, Sacramento, Ca.