High-density element concentrations in fish from subtidal to hadal zones of the Pacific Ocean

Abstract

Anthropogenic use of high density, toxic elements results in marine pollution which is bio-accumulating throughout marine food webs. While there have been several studies in various locations analyzing such elements in fish, few have investigated patterns in these elements and their isotopes in terms of ocean depth, and none have studied the greatest depth zones. We used a flame atomic absorption spectrophotometer-hydride system and an inductively coupled plasma-mass spectrometer to determine concentrations of the high-density elements arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), plus the light-metal barium (Ba), in fish ranging from bathyal (1000 m in Monterey Bay) to upper hadal zones (6500-7626 m in the Kermadec and Mariana Trenches) in the Pacific Ocean. Five species of fish-including the Mariana Trench snailfish, the world's deepest known fish newly discovered-were analyzed for patterns in total element concentration, depth of occurrence, Se:Hg ratio, plus mercury isotopes in the deepest species. Co and As levels decreased with depth. In the Mariana Trench, Pb, Hg, Cd, and Cu were higher than in all other samples, and higher in those plus Ba than in the Kermadec Trench. The latter samples had far higher Ni and Cr levels than all others. Mercury relative isotope analysis showed no depth trends in the deepest species. Se:Hg showed a large molar excess of Se in bathyal flatfish species. These patterns indicate that exposures to pollutants differ greatly between habitats including trenches of similar depths.

Keywords: Biogeoscience; Earth sciences; Environmental science; Geochemistry; Oceanography.

Fig. 1

High-density element concentrations (plus barium) in fish muscle from each sample collection site. Error bars are standard errors. Note the very large ordinate scale change for As in panel A for the Aleutian study (Burger et al., 2014; N/A = not analyzed in that study), and the large scale change for Cr and Ni in panel D.

Fig. 2

Concentrations of Arsenic (A) and Cobalt (B) in fish muscle by collection depth (with deepest specimens at bottom left of plot). Note the very large scale change for ng/g in panel A. N/A = not analyzed in the Aleutian study (Burger et al., 2014). Error bars are standard errors; **indicates statistically higher than all other groups (P < 0.001); *statistically higher than other groups but lower than **group (P < 0.05).

Fig. 3

Concentrations of Mercury (A) and Copper (B) by collection depth as in Fig. 2. N/A = not analyzed in Aleutian study (Burger et al., 2014). Error bars are standard errors; *, ** indicate statistics as in Fig. 2; †† indicates statistically lower than all other groups (P < 0.05).

Fig. 4

Concentrations of Nickel (A) and Chromium (B) by collection depth as in Fig. 2. N/A = not analyzed in Aleutian study (Burger et al., 2014). Note the large scale change for ng/g in both panels. Error bars are standard errors; **indicates statistics as in Fig. 2.

Fig. 5

Concentrations of Barium (A), Cadmium (B), and Lead (C) by collection depth as in Fig. 2. N/A = not analyzed in Aleutian study (Burger et al., 2014). Error bars are standard errors; **, †, †† indicate statistics as in Fig. 2 except for barium (panel A) where ** indicates P = 0.05.

Fig. 6

Relationship between total Se concentration and total Hg concentration in subtidal and bathyal flatfish. Red circles are Dover Sole; red squares are the Deep Sea Sole; the diamond is the flatfish value from the Aleutian study (Burger et al., 2014).

Fig. 7

Relative mercury isotope ratios in delta notation (see Introduction) plotted with depth of samples for Δ199 Hg (A), δ199 Hg (B), δ201 Hg (C), δ202 Hg (D) and Δ201Hg (E). The green circles are samples from the Kermadec Trench, the blue circles from the Mariana Trench.

Fig. 8

Relationships between mercury relative isotope ratios in delta notation (see Introduction) for Δ199 vs δ202 Hg (A) and Δ201 Hg (B). The green circles are samples from the Kermadec Trench, the blue circles from the Mariana Trench.