Changes in polychlorinated biphenyl (PCB) exposure in tree swallows (Tachycineta bicolor) nesting along the Sheboygan River, WI, USA

Abstract

Exposure to polychlorinated biphenyls (PCBs) in tree swallow (Tachycineta bicolor) eggs on the Sheboygan River, Wisconsin in the 1990s was higher at sites downstream (geometric means = 3.33-8.69 μg/g wet wt.) of the putative PCB source in Sheboygan Falls, Wisconsin than it was above the source (1.24 μg/g) with the exposure declining as the distance downstream of the source increased. A similar pattern of declining exposure was present in the 2010s as well. Although exposure to PCBs in eggs along the Sheboygan River at sites downstream of Sheboygan Falls has declined by ~60 % since the mid-1990s (8.69 down to 3.27 μg/g) there still seems to be residual pockets of contamination that are exposing some individuals (~25 %) to PCB contamination, similar to exposure found in the 1990s. The exposure patterns in eggs and nestlings among sites, and the changes between the two decades, are further validated by accumulation rate information.

Concentrations and spatial patterns of organic contaminants in tree swallow (Tachycineta bicolor) eggs at United States and binational Great Lakes Areas of Concern, 2010–2015

“…For 3 chemical classes (PCBs, PCDD-Fs, and PBDEs) and 7 other organochlorine contaminants considered in the present study, nearly all of the sites were either at or below background, below average concentrations at non-AOCs, or below the mean at the most contaminated non-AOC. Geometric mean total PCBs at approximately 70% of sites (78% of AOCs) were below either the means at the most contaminated non-AOC (1.30 mg/g) in the present study or the maximum reference value (1.74 mg/g [32]) from those described in the literature. This, combined with the documented reduction in exposure to PCBs [13,30,32] in tree swallow eggs over the past 20 yr and declining PBDEs [44,45] in osprey egg samples, is a promising development.…”

“…Fifteen of the 59 sites within AOCs (25%) were at or below background, and 69% of sites ( n = 41) were at or below mean concentrations at the most PCB‐contaminated non‐AOC site (Little Tail Point, with 1.30 μg/g wet wt). Of sites within AOCs, 78% had mean concentrations less than the mean reference high concentration (1.74 μg/g ).…”

“…A background PCB concentration (0.34 mg/g wet wt) was determined by calculating the geometric mean for PCB concentrations measured at multiple reference sites from tree swallow studies conducted across the United States and Canada [3,4,[23][24][25][26][27][28][29][30][31]; the range in mean background concentrations was between 0.13 mg/g and 1.74 mg/g wet weight. Approximately 30% (29.6%) of AOCs had geometric mean PCB concentrations at or below mean background exposure ( Figure 2); 78% of AOCs had a mean exposure less than the mean at the most contaminated non-AOC location (Little Tail Point, 1.30 mg/g) or the highest mean at US and Canadian reference sites (1.74 mg/g [32]). There were statistical differences among locations ( Figure 2; p < 0.001, df 36,364 , F ¼ 26.56); most locations did not differ from their nearest neighbors along the x axis but did differ from more distant locations along the x axis.…”

Latent cognitive effects from low‐level polychlorinated biphenyl exposure in juvenile European starlings (Sturnus vulgaris)

“…In contrast, the control group had a mean liver residue of 0.69 mg/g, consistent with background concentrations that are typically less than 1 mg/g in eggs and nestlings [50,51]. Reproductive effect levels in birds are known to occur at egg PCB concentrations of 13.6 mg/g wet weight (starlings), 20 mg/g wet weight (tree swallows), 35 mg/g wet weight (raptors), and 23 mg/g wet weight to 142 mg/g wet weight (gulls and terns) [2,24]. It should be noted, however, that comparisons of effect levels associated with egg versus liver concentrations are uncertain.…”

“…Although thyroid function may be less susceptible to PCB disruption in birds than in mammals , adverse consequences associated with early developmental exposure have been reported. Reduced egg quality, low hatching success rates, abnormal nestling morphology, decreased nestling survival, and reduced posthatching weights are examples of consequences associated with developmental PCB exposure in songbirds .…”