Overview
This paper measured total mercury (THg) in fish muscle and both THg and methylmercury (MeHg) in terrestrial and aquatic invertebrates from a small stream-riparian food web on the Big Sur coast of California, where marine fog is a known vector of ocean-derived MeHg to terrestrial ecosystems. The study found that mean THg in age 0 (young-of-year) trout was 400 ng/g dw, rising to 1200–1300 ng/g dw in age 1+ trout and sculpin, with a maximum individual THg exceeding 3500 ng/g dw. Terrestrial invertebrates had mean MeHg concentrations three to four times higher than aquatic invertebrates of the same trophic level, with some centipede and scorpion individuals exceeding 1000 ng/g dw MeHg — a finding the authors attribute to marine fog as a delivery pathway for ocean-derived MeHg into coastal terrestrial food webs.
Key numbers
Fish (muscle tissue, dry weight basis):
- Age 0 trout (n=10, 72–90 mm): mean THg 400 ng/g dw
- Age 1+ trout (n=10, 125–300 mm): mean THg 1200–1300 ng/g dw; maximum individual >3500 ng/g dw
- Coastrange sculpin (n=10, 86–128 mm): mean THg 1200–1300 ng/g dw (similar to age 1+ trout)
- Conversion from dry to wet weight assumed 25% moisture (dry:wet = 1:4), yielding approximate wet weight equivalents of ~100 ng/g ww for age 0 trout and ~300–325 ng/g ww for age 1+ trout and sculpin
Invertebrates (dry weight basis, Table 1 in source):
- Aquatic detritivore/herbivore THg range: 13–70 ng/g dw (stoneflies, caddisflies, mayflies)
- Aquatic predator insects (dobsonflies, dragonflies): mean THg 85–120 ng/g dw
- Terrestrial detritivores (isopods, diplopods): mean THg 200–500 ng/g dw; %MeHg ~50–80%
- Terrestrial predators (centipedes, scorpions): individual samples >1000 ng/g dw MeHg
Methods (brief)
Fish were archived muscle samples from incidental mortalities in electrofishing surveys (2005–2019). Invertebrates collected by hand search in summer 2020. THg analyzed by Milestone DMA-80 direct mercury analyzer, EPA Method 7473. MeHg analyzed by KOH/methanol extraction, derivatization with sodium tetraethylborate, GC-CVAFS, EPA Method 1630. Certified reference materials run daily; recoveries 96–114% for THg CRMs and 90% for DORM-4 MeHg. Samples for fish expressed as muscle THg, converted to wet weight using 25% dry weight assumption.
Implications
Certification: freshwater salmonid products from coastal California fog zones may carry substantially elevated MeHg, warranting geographic origin disclosure and lot-level testing. Age-related bioaccumulation is strong (3x increase from age 0 to age 1+ trout). Fog-belt coastal sourcing is a meaningful variance factor.
Courses: illustrates marine-fog MeHg pathway as an underappreciated contamination route distinct from aquatic sediment methylation.
App: trout from coastal California should carry a MeHg risk flag; geographic provenance is a key variable.
Related evidence
Update history
No substantive edit history is available in this build. The full commit record is available in git.