Background Concentrations of Heavy Metals in Brown Algae from the Northwest Sea of Japan

Background concentrations of Fe, Mn, Cu, Zn, Pb, Cd, and Ni were calculated for brown algae Costaria costata from the northwest Sea of Japan. Also the paper contains refined data on heavy metal concentrations in the widespread distributed brown algae, such as Stephanocystis crassipes, Sargassum pallidum and S. miyabei. As the upper threshold levels of metal background concentrations, the median values plus double medians of absolute deviations from the medians were used (Me + 2MAD). The lower threshold level of the background concentration equal to the physiological need for an element is the median of 15% minimum values in the sampling minus the double median of absolute deviations from the median (Me 15 − 2MAD 15 ). The calculated ranges of the background concentrations of metals in algae were compared with concentrations of elements in macrophytes collected from habitats with background concentrations of metals in water.


Introduction
Sustainable use of the sea coast and coastal waters implies the comprehensive assessment of this natural-technogenic system. Heavy metals are one of the most toxic groups of contaminants. In order to estimate the heavy metals pollution, both data of direct chemical analysis, data on metal concentration in the bottom sediments and dominant benthic organisms-bivalves and algae-used in the world (Goldberg, Bowen, Farrington, Harvey, Martin, Parker et al., 1978;Rainbow & Phillips, 1993;Jayasekera & Rossbach, 1996, et al.). Biomonitors accumulate metals from the environment with natural characteristics with consideration DOI: 10.4236/gep.2020.810011 148 Journal of Geoscience and Environment Protection for their own needs (Chernova & Shulkin, 2019) and, in the presence of the elevated concentrations, in proportion to their content in the environment (Jayasekera & Rossbach, 1996). However, the sanitary and hygienic standards rather than environmental ones of the toxic element concentrations in organisms were set. These sanitary and hygienic standards are designed for provision of safety of foods and raw materials but they are also used as the criteria for evaluation of the hydrobionts life environment state which is wrongful. Another approach to the assessment of metal pollution of the aquatic area using the hydrobionts is based on comparison of the obtained concentrations in the indicator organisms from the study habitat area with the "supposedly-background" concentrations in organisms from the "supposedly-clean" habitats.  (Cantillo, 1998). As the threshold concentration of metals in mussels and oysters, the authors of the program have taken 85 percentile of sampling. Scanes and Roach (1999) (Reinmann, Filzmoser, & Garrett, 2005;Lukashev, 2007). This method can be used both with a normal distribution of sampling and in its absence. The purpose of this article is to determine the background and threshold concentrations of metals in brown algae Costaria costata from the coastal waters of the Russian part of the Sea of Japan and to refined data for other widespread distributed macrophytes.

Data
We used data on microelement concentrations in samplings of widespread brown algae species from Laminariaceae (Costaria costata) and Sargassaceae 85˚C. The further sample preparation was performed in accordance with method published earlier (Chernova & Kozhenkova, 2016) in the Pacific Geographical Institute, FEB RAS.
Samplings of C. costata from 42 stations, S. miyabei from 97 stations, S. pallidum from 72 stations, and S. crassipes from 46 stations were treated for statistical analysis of metal concentrations in the thalli of brown algae.

Methods
The descriptive statistics was created with Excel software; the normal distributions of metal concentrations and metal concentration logarithms were verified using the critical coefficients of asymmetry and excess (Lakin, 1990). After discarding the statistic outliers being beyond the range of normal or lognormal distribution, the values of Me ± 2МАD were calculated for residual sample. The The calculated ranges of the background concentrations of metals in algae were compared with concentrations of elements in macrophytes collected from habitats with background concentrations of metals in water (Shulkin, 2004;Shulkin, Orlova, Shevchenko, & Stonik, 2013).

Results and Discussion
The background is the microscale stable level of the environment state on which the local natural and anthropogenic impact features are placed. In the geochemistry, the arithmetic mean value (under conditions of normal distribution) or geometric mean (for other types of concentration distribution) in samples is taken as the background value of the chemical element concentration in the natural object (Reinmann, Filzmoser, & Garrett, 2005;Lukashev, 2007). The background concentration of an element in living organisms is the sum of the physiologically needed amount of the element and some nontoxic excess accumulated from the environment with the regional background level of microelement to which the organisms are adapted (Chernova & Khristoforova, 2008;Chernova, Khristoforova, & Gonokhov, 2009 trations. This is caused by the genetic heterogeneity of a population and the presence of several hypo-and hyper-concentrators of chemical elements (Lobel & Wright, 1983). The lower limit of concentrations should conform to the minimum physiological amount for essential elements (Cu, Zn, Ni, Fe, and Mn) and zero concentration of nonessential ones (Pb and Cd). In view of this, the background concentration of a microelement in organisms must fall in a definite range of values. The upper limit of background values should conform to a limiting value of the element concentration in organism to which the species is adapted to the geochemical conditions (Ermakov & Tyutikov, 2008).
The method of calculation of the threshold value as median plus double median of absolute deviations from the median (Med + 2МАD) and background (median) was used in the samples of algae (Chernova, 2012;Chernova & Kozhenkova, 2016). In this work, the threshold concentrations of metals in Costaria costata were calculated, and those in Stephanocystis crassipes were refined. The background concentrations of Pb in Sargassum species were refined also (Table   1). Me 15 ± 2MAD 15 , a median of microelement concentrations from 15% of the least values of the sampling (Table 2) Table 2).
Comparison of these values with the empirically obtained background concentrations of elements in algae (Fe, Mn, Cu, Zn, Ni) (Kozhenkova, 2000) has shown that they are similar. The assessed values of the "natural background" for Cd and Pb appeared to be lower than those empirically obtained using the data of the 20th century, which is possibly related to the difficulties of their determination in previous years. The lower threshold levels of background concentrations    (Chernova, 2016). The concentration of manganese in organisms, the same as that of iron, depends on the proximity to the sources of terrigenous runoff. The algae from the Sea of Japan have also distinguished by the greater value of Me 15 ± 2MAD 15 for Zn and Cd due to the lower biomass in coastal zone of the Sea of Japan (littoral and upper sublittoral). Biomass actively extracts essential zinc and its chemical counterpart cadmium from water for its physiological needs (Chernova, 2016).
According to the directly proportional relationship between the metal content in water and organisms, organisms must accumulate background concentrations of elements under background conditions. For the coastal waters of the northwest Sea of Japan, the following concentrations of the dissolve metals in the sea water were proposed as background concentrations: Zn-0.5 -0.8; Cu-0.3 -1.2; Pb-0.05 -0.1; Cd-0.04 -0.05; Fe-1 -10 and Mn-2.6 -20 µg/l (Shulkin, 2004;Shulkin, Orlova, Shevchenko, & Stonik, 2013). The consistence between concentrations of metals in algae and in sea water was studied (Chernova & Shulkin, 2019) and it was shown that the macrophytes in which the concentrations of metals do not exceed the threshold levels (Med + 2MAD) grow in the habitats with the background metal concentrations in water (Table 3). The exception is provided by some data on Fe, which prevails in water mainly in suspended form (Shulkin, 2004) and can be adsorbed onto the thalli surface and to increase the metal concentrations in algae.  In brackets the threshold metal concentration in algae (Chernova & Kozhenkova, 2016); n.d., no data.
or 5 -10 µg/g of dry weight. As we can see (Table 1)