4.1. Fish Samples
The minimum, the maximum, and the average 210Po concentrations for the mullet are 1.49 ± 0.34 Bq·kg−1 (February), 9.42 ± 0.92 Bq·kg−1 (October), and 5.00 ± 0.65 Bq·kg−1, respectively. The minimum, the maximum, and the average 210Pb concentrations for mullet are ND (non-detectable), 1.16 ± 0.31 Bq·kg−1 (March), and 0.99 ± 0.30 Bq·kg−1, respectively.
For sea bass, the minimum, the maximum, and the average
210Po concentrations are 3.58 ± 0.46 Bq·kg
−1 (December), 4.71 ± 0.58 Bq·kg
−1 (March), and 4.06 ± 0.64 Bq·kg
−1, respectively. For sea bass the minimum, the maximum, and the average
210Pb concentrations are ND, 1.47 ± 0.23 Bq·kg
−1 (February), and 1.12 ± 0.44 Bq·kg
−1, respectively. Strok and Smodis [
15] measured the
210Po and
210Pb activities as 0.37 ± 0.07 Bq·kg
−1 and 2.85 ± 0.48 Bq·kg
−1, respectively. The researchers stated that
210Pb activity concentrations for marine species are usually lower than
210Po activity concentrations. However, they found an exception to this for sea bass. They concluded that it is due to the terrestrial feeding habit in mariculture. In Portugal, Malta et al. [
16] studied the radioactivity levels for sea bass. They found the mean
210Po activity concentrations as 13 ± 7, 3.8 ± 3.1, 0.53 ± 0.52 Bq·kg
−1 in liver, gonads, and muscle of mullets, respectively. They determined the mean
210Pb activities in liver, gonads, and muscle of mullets as 1.39 ± 0.87, 0.32 ± 0.34, and 0.10 ± 0.09 Bq·kg
−1.
For eel, the minimum, the maximum, and the average
210Po concentrations are 4.05 ± 0.84 Bq·kg
−1 (May), 12.56 ± 1.62 Bq·kg
−1 (March), and 6.51 ± 0.91, respectively. For eel, the minimum, the maximum, and the average
210Pb concentrations are ND, 2.66 ± 0.34 Bq·kg
−1 (February), and 1.58 ± 0.27, respectively. Al-Masri et al. [
17] found the
210Po and
210Pb concentrations for eel in Syria as 1.03 ± 0.003 Bq·kg
−1 and 0.005 ± 0.001 Bq·kg
−1, respectively.
Cr, Ni, Pb, Cd, Mn, Fe, and Zn levels in the fish samples measured and are given in
Table 1 with data from around the world. According to Turkish Food Regulations, the maximum Cd, Pb, and Zn concentrations should not exceed 0.05, 0.3, and 50 mg·kg
−1, respectively. The observed values in this study do not exceed the given limits. The high concentrations can be linked to the industrial facilities on the Büyük Menderes River, which is the largest water source for Lake Bafa.
The dose values are presented in
Table 2. The calculated annual effective ingestion dose for humans due to
210Po from the consumption of the lake fishes ranges from 0.011 to 1.169 µSv·y
−1. It is clear that the highest dose value (1.169 µSv·y
−1) was observed of mullet. According to the UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) [
18] report, the effective dose equivalent of
210Po in areas of normal background radiation is approximately (130 µSv·y
−1). This dose value is higher than the doses that were found in this study.
4.2. Surface Sediment
The points where the surface sediment samples collected are shown in
Figure 2. The average
210Po concentrations for surface sediment samples in summer, autumn, winter, and spring are 113 ± 9 Bq·kg
−1, 128 ± 9 Bq·kg
−1, 135 ± 9 Bq·kg
−1, and 134 ± 9 Bq·kg
−1, respectively.
The average 210Pb concentrations for surface sediment samples in summer, autumn, winter, and spring are 56 ± 6 Bq·kg−1, 58 ± 7 Bq·kg−1, 111 ± 13 Bq·kg−1, and 46 ± 5 Bq·kg−1, respectively.
The average
210Po and
210Pb values are given in
Figure 3 seasonally.
There are significant seasonal differences in
210Pb concentrations. The highest
210Pb concentrations were observed in the winter. The sampling station is under the influence of Mediterranean climate with cool wet winters and warm to hot, dry summers. Most of the precipitation falls during the winter months. It is believed that the elevated concentrations of
210Pb in sediments in winter could be linked to high atmospheric deposition of
210Pb during this season [
25].
The
210Po:
210Pb activity ratios in surface sediments samples varies between 0.85 and 4.48 as shown in
Table 3, with a mean value of 2.14. There are significant differences in
210Po and
210Pb concentrations with respect to different seasons. These differences could be due to the local pollution sources as well as variations in the riverine and rainfall regimes.
4.3. Core Sample
The minimum, the maximum, and the average 210Po concentrations in core samples were found to be 32 ± 1 Bq·kg−1 (at 33 cm), 362 ± 20 Bq·kg−1 (at the surface), 116 ± 5 and Bq·kg−1, respectively. The minimum, the maximum, and the average 210Pb concentrations in core samples were found to be 14 ± 2 Bq·kg−1 (at 34.2 cm), 201 ± 18 Bq·kg−1 (at 1.2 cm), and 71 ± 8 and Bq·kg−1, respectively.
Figure 4 shows
210Pb
ex activity concentrations on a logarithmic scale versus cumulative mass depth. Activity concentration of excess
210Pb varies exponentially along the sediment profile. The respective maximum concentration (159 ± 18 Bq·kg
−1) was measured in the 1.2 cm sediment layer. The equilibrium point is at 12.6 cm. The
210Pb concentration in the core sample decreases with depth, so the
210Pb flux of the sediment is constant. The age of the sediment layers was calculated with the CRS model. The results are given in
Table 4. The deepest sediment layers, at depths between 31.8 and 33 cm, had been deposited around the beginning of the 1900s.
In the study, the sediment mass accumulation rate was found to be 3.27 g·m
−2·day
−1 (0.119 g·cm
−2·y
−1). The sedimentation mass accumulation rate in Lake Bafa is relatively lower than Lake Hachirogata and Lake Erie. Jin et al. [
26] found the sediment mass accumulation rate in Lake Hachirogata 0.43 g·cm
−2·y
−1 and 0.45 g·cm
−2·y
−1 in two core samples, and Klump et al. [
27] determined the accumulation rate in an average of 0.23 g·cm
−2·y
−1 for Lake Erie.
The heavy metal concentrations in vertical profile of samples from the core are given in
Table 5. For all the metals investigated, there is a peak value at 16 cm and below this point the concentrations are decreasing with depth. Except Fe and Zn, the highest and lowest concentrations are at 16 cm and 4.5 cm, respectively. This coincides with the beginning of industrialization in the region. The measured concentration of Fe and Zn are in the range 3.11%–4.13%, 68–90 ppm, respectively. The Zn concentrations in the core sample are lower than the ERL (effects range low) and ERM (effects range median) limits [
28] (
Table 6). High Fe and Zn concentrations were observed at 3 and 6 cm. The measured concentration of Cd and Pb are in the range 0.09–0.20 ppm, 8.3–19.1 ppm, respectively. Cd and Pb concentrations show a similar pattern. The concentrations of both metals are below the ERL limits. The measured concentration of Cr and Ni are in the range of 214.4–288.3 ppm, 297.2–457.9 ppm, respectively. While the Cr concentrations are between the ERL and ERM limits, Ni concentrations are higher than the ERM limit.