Research Findings
Experiment 1: Initial Findings
Methodology
Brine shrimp cysts were exposed to octisalate (dissolved in cyrene) using serial dilution (1/1, 1/10, 1/100, and 1/1000) with saline-only and cyrene-only control solutions. After a 5-day refrigeration period and 48-hour room temperature rest, hatch rates were calculated by counting live brine shrimp in 25 droplets using a magnifying glass.
Results
The highest concentration (1/1) showed a significant 66% decrease in hatch rate compared to the saline-only control. The 1/10 treatment showed no significant change, while the 1/100 treatment showed a 32% increase and the 1/1000 treatment showed an 18% decrease in hatch rate. Visual inspection revealed sluggish movement in the 1/1 concentration group.
Conclusion
High concentrations of octisalate appear to reduce brine shrimp hatch rates significantly, though the relationship with milder concentrations remains unclear and requires further investigation.
Experiment 2: Follow-up Study
Methodology
Using an improved methodology, brine shrimp cysts were again exposed to octisalate (dissolved in cyrene) at the same dilutions (1/1, 1/10, 1/100, and 1/1000). This time, bleach-only and cyrene-only solutions served as controls. The experimental setup was similar, but 85µl droplets were measured with micropipettes and counted using a dissecting scope for improved accuracy.
Results
Unexpectedly, all test concentrations showed an increase in hatch rate compared to controls: 7.1% increase for 1/1 concentration, 13.2% increase for 1/10, 2.3% increase for 1/100, and 9.7% increase for 1/1000. The positive control with bleach showed 100% mortality (no eggs hatched).
Conclusion
The revised experiment suggests no statistically significant relationship between octisalate concentration and brine shrimp hatch rate at the ranges tested, contradicting the first experiment's findings and highlighting the need for more refined testing methodologies.
Research Implications
While these experiments provide mixed results regarding octisalate's impact on brine shrimp hatch rates, it's important to note that other research has shown population decline in flatworms and pulse coral when exposed to sunscreens containing octisalate[2]. Additionally, octisalate is known to negatively affect other aquatic larvae at later developmental stages[3].
These findings underscore the complexity of environmental toxicology and suggest that hatch rate alone may not be a sufficient metric for evaluating ecological impact. Further research with improved methodologies is needed to fully understand how sunscreen chemicals affect marine ecosystems.