Environmental context and contaminant biotransport by Pacific salmon interact to mediate the bioaccumulation of contaminants by stream-resident fish

Pacific salmon as vectors of environmental contaminants: An experimental test confirms synoptic surveys in natural streams

Pacific salmon transfer large quantities of material to tributaries during their spawning migrations, including carcass tissue and labile nutrients but also persistent organic pollutants (POPs) and heavy metals. We conducted a Before-After-Control-Intervention experiment by adding salmon carcasses and eggs to a Michigan (USA) stream that had never received inputs from non-native salmon to understand the bioaccumulation and persistence of biotransported contaminants. Our experimental outcomes were compared to previous studies using meta-analysis. Coincident with the introduction of salmon, the PCB and DDE burden of resident trout significantly increased. However, we did not observe changes in total mercury (Hg). Two years after the salmon addition experiment concluded, resident trout POP concentrations had returned to pre-addition levels, with no difference between the treatment and control reaches. Analysis of effect sizes suggested that the contaminant response observed in our experiment is consistent with field survey observations. Our study suggested that the consumption of salmon eggs drove the increase in POP burden of resident trout while Hg bioaccumulation was influenced by watershed sources. Critically, our study suggests that ecosystems are capable of quickly recovering from POP inputs from species migrations if contaminant sources are removed.

Understanding drivers of mercury in lake trout (Salvelinus namaycush), a top-predator fish in southwest Alaska's parklands

Mercury (Hg) is a widespread element and persistent pollutant, harmful to fish, wildlife, and humans in its organic, methylated form. The risk of Hg contamination is driven by factors that regulate Hg loading, methylation, bioaccumulation, and biomagnification. In remote locations, with infrequent access and limited data, understanding the relative importance of these factors can pose a challenge. Here, we assessed Hg concentrations in an apex predator fish species, lake trout (Salvelinus namaycush), collected from 14 lakes spanning two National Parks in southwest Alaska, U.S.A. We then examined factors associated with the variation in fish Hg concentrations using a Bayesian hierarchical model. We found that total Hg concentrations in water were consistently low among lakes (0.11-0.50 ng L-1). Conversely, total Hg concentrations in lake trout spanned a thirty-fold range (101-3046 ng g-1 dry weight), with median values at 7 lakes exceeding Alaska's human consumption threshold. Model results showed that fish age and, to a lesser extent, body condition best explained variation in Hg concentration among fish within a lake, with Hg elevated in older, thinner lake trout. Other factors, including plankton methyl Hg content, fish species richness, volcano proximity, and glacier loss, best explained variation in lake trout Hg concentration among lakes. Collectively, these results provide evidence that multiple, hierarchically nested factors control fish Hg levels in these lakes.

Seasonal distribution pattern and bioaccumulation of Polycyclic aromatic hydrocarbons (PAHs) in four bioindicator coastal fishes of Argentina

Polycyclic aromatic hydrocarbons (PAHs) are pollutants of global concern in coastal environments. They have a wide range of biological toxicity and due to their inherent properties, can easily bioaccumulate in organisms and concentrate in the environment. This work evaluated, in an integrated way, the seasonal PAH distribution patterns in sediments and four bioindicators fish species in a highly impacted estuary of Argentina; besides, their bioaccumulation patterns were assessed for the first time as indicator of ecological risk. The highest PAH levels in fish were found for Ramnogaster arcuata with an average of 64 ng g^-1 w.w., followed by Micropogonias furnieri (45 ng g^-1 w.w.), Cynoscion guatucupa (28 ng g^-1 w.w.), and Mustelus schmitti (16 ng g^-1 w.w.). Fish presented the highest PAH levels in fall with a predominance of petrogenic PAHs in colder seasons and pyrolytic PAHs in warmer seasons. Sediments presented an average of 233 ng g^-1 d.w. with the same seasonal composition pattern of the fish tissues. Additionally, the data suggested that the main source of PAHs are wastewater discharges. The bioaccumulation factor (BAF) of PAHs in the tested fishes were found to range from 0.3 to 8. The highest values were observed during fall and winter, while bioaccumulation did not occur in moist spring and summer samples, which would suggest a high biotransformation process during these seasons. Results suggested that class III of juvenile C. guatucupa and M. furnieri, and adults R. arcuata are more sensitive bioindicators of chronic PAH contamination and that their bioaccumulation is independent of the compound hydrophobicity; this could have a positively influence on the criteria used for biological monitoring programs along the Atlantic coast. In addition, the presented BAF data on the target species will serve as a useful pollution indicator for South Atlantic coastal fish.

Enhanced bioaccumulation of fluorinated antibiotics in crucian carp (Carassius carassius): Influence of fluorine substituent

The negative impact of residual fluorinated antibiotics on the ecosystem and human health are of great concern. However, only a few studies have been conducted on the factors that influence the bioaccumulation of fluorinated antibiotics in aquatic organisms. To investigate the effects of fluorine substituent, environmental concentration of antibiotics, and temperature on the bioaccumulation of florfenicol (FLO), thiamphenicol (TAP), ofloxacin (OFX), and pipemidic acid (PPA), crucian carp (Carassius carassius) were exposed to different concentrations of antibiotics and different temperatures for 21 days. The liver exhibited the highest antibiotic concentrations, with 315.4 ± 13.6 ng g^-1 wet weight (ww), followed by the bile (279.4 ± 12.4 ng mL^-1), muscle (53.1 ± 4.3 ng g^-1 ww), and gills (37.1 ± 2.6 ng g^-1 ww). The FLO and OFX containing the fluorine substituent were much easier to accumulate in crucian carp compared with their isonomic TAP and PPA, respectively. The fluorine substituent increased the bioaccumulation of the targeted antibiotics in crucian carp. In addition, the lower levels of antibiotics presented higher bioaccumulation potential, but the temperature had little effect on the bioaccumulation. These findings in the present study can provide further insight into the environmental behaviors and ecological risks of fluorinated antibiotics in the aquatic environment.

Biotransport of persistent organic pollutants in the southern Hemisphere by invasive Chinook salmon (Oncorhynchus tshawytscha) in the rivers of northern Chilean Patagonia, a UNESCO biosphere reserve

Biotransport is often associated with migration patterns of species, including large, anadromous salmonids. Several studies have reported biotransport of persistent organic pollutants in the Northern Hemisphere, but there is no published information on biotransport ocurring south of the equator. Chile's Patagonia is one of the last largely intact natural areas in the world. The objective of this study was to determine whether persistent organic pollutants are transported by the invasive Pacific Chinook salmon (O. tshawytscha) from the Pacific Ocean to Chilean Patagonia. Samples of juvenile and adult Chinook salmon were analyzed for polychlorinated biphenyls, pesticides and polybrominated diphenyl ethers. The results revealed that concentrations of POPs in adults migrating into Patagonian rivers were significantly higher than those found in juveniles migrating seaward. A mass balance analysis indicates that Chinook salmon are a source of persistent organic pollutants to Chilean Patagonia inland waters. Capsule: Biotransport of Persistent Organic Pollutants (POPs) by Chinook salmon (O. tshawytscha) from the Pacific Ocean to Chilean Patagonia has been confirmed by mass balance of POPs.

Species-Specific Characteristics Influence Contaminant Accumulation Trajectories and Signatures Across Ontogeny in Three Pelagic Shark Species

Factors influencing organic contaminant accumulation in sharks, especially across ontogeny, are not well-known. Contaminant concentrations were measured in three species of sharks (Blue, Shortfin Mako, and Common Thresher) across a range of size classes (neonatal to adult) that vary in their ecological and physiological characteristics. Empirical data was compared to a theoretical framework that predicted the shape of lifetime accumulation curves. We found that a one-size-fits-all accumulation model was not appropriate as species-specific characteristics had a significant effect on contaminant accumulation trajectories. Maternal offloading likely has an important effect on determining neonatal shark contaminant starting points, and trophic ecology and physiology may interact to affect the shape of species' contaminant accumulation curves. Makos were found to have the highest accumulation potential and Blues the lowest, with Threshers being intermediate in accumulation potential. Changes in species' ecology and/or physiology were also reflected in contaminant signature changes over ontogeny. If contaminant concentrations are to be used as a proxy for risk, species-specific characteristics need to be taken into account when estimating contaminant exposure and its potential negative effects on shark health and human consumption safety.

Using a dynamic bioenergetics-bioaccumulation model to understand mechanisms of uptake and bioaccumulation of salmon-derived contaminants by stream-resident fish

Ecosystem linkages created by migratory organisms such as Pacific salmon (Oncorhynchus spp.) facilitate the transfer of ecologically beneficial resource subsidies and environmentally damaging contaminants to recipient food webs. In the Laurentian Great Lakes, introduced Pacific salmon accumulate large contaminant burdens that they disperse to streams during spawning in the form of carcass and gametic tissue, with uncertain consequences for stream food webs. Here, we describe a coupled bioenergetics-bioaccumulation model parameterized using empirical and literature-sourced data to predict the dual effect of Pacific salmon on stream-resident brook trout (Salvelinus fontinalis) growth and contaminant bioaccumulation. Within the model, we developed four unique scenarios to ascertain how the (1) trophic pathway to contamination, (2) level of salmon egg consumption, (3) intensity and duration of salmon exposure, and (4) age of first exposure to salmon, affected growth and contaminant bioaccumulation in brook trout. Our model demonstrated that salmon egg consumption increased brook trout growth and PCB bioaccumulation while reducing Hg tissue concentrations. Other trophic pathways, including direct carcass consumption and an indirect food web pathway, did not strongly influence growth or contaminant bioaccumulation. Our model also demonstrated that variation in the magnitude and temporal duration of salmon egg consumption mostly strongly influenced the growth and contaminant concentration of younger brook trout. Overall, our model highlighted that Pacific salmon transfer energy and contaminants but this balance is dictated by the food web pathway and plasticity in the diet of stream-resident fish. Our mechanistic, model-based evaluation of salmon contaminant biotransport can be extended to predict the impact of other migratory fishes on recipient food webs.