**1. Introduction**

Cow milk is considered a nearly complete food because of its high content of protein, fat, and essential minerals, yet the potential presence of contaminants in milk constitutes a health concern. This is particularly true in light of the fact that cow milk is one of the main constituents of the daily diet in many countries, especially for vulnerable groups, infants, and elderly people [1]. Guidelines from the European Union Common Agricultural Policy aim to ensure a high level of food safety and animal health through coherent "farm to fork"

**Citation:** Forcada, S.;

Menéndez-Miranda, M.; Boente, C.; Rodríguez Gallego, J.L.; Costa-Fernández, J.M.; Royo, L.J.; Soldado, A. Impact of Potentially Toxic Compounds in Cow Milk: How Industrial Activities Affect Animal Primary Productions. *Foods* **2023**, *12*, 1718. https://doi.org/10.3390/ foods12081718

Academic Editors: Dapeng Peng and Yongzhong Qian

Received: 14 March 2023 Revised: 14 April 2023 Accepted: 18 April 2023 Published: 20 April 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

measures and adequate monitoring. This necessitates exhaustive characterization of farms at different levels of the production chain.

In the case of dairy farms, this characterization includes the milk and even the soil where crops are cultivated for animal forage (feed forage). Many dairy farms in northern Spain, for example, produce their own forage crops as a traditional practice [2], and foragebased animal nutrition depends strongly on local geographical conditions [3]. The growth of cities and industrial expansion means that many farms lie near cities or industrial zones that emit pollutants into the atmosphere and wastewater. This increases the risk of soil contamination, potentially compromising animal food safety. In fact, hazardous compounds in the soil can pose a risk to animals and to humans who consume animalderived products [4,5].

Potentially toxic elements (PTEs), mainly heavy metals and metalloids, pose a growing hazard in the environment [6]. Those elements named as heavy metals are referred to by their high atomic mass and density. Their persistence in the soil, reflecting their resistance to degradation, makes them the most dangerous group of inorganic contaminants. While the PTEs iron (Fe), cobalt (Co), copper (Cu), manganese (Mn), molybdenum (Mo), and zinc (Zn) are essential for humans and cattle in trace amounts, they are toxic at higher concentrations [7,8]. The PTEs arsenic (As), mercury (Hg), cadmium (Cd), and lead (Pb) are considered toxic even at low concentrations and can cause serious illness if they accumulate in an organism [8]. PTEs can enter the food chain by first entering the soil from the atmosphere or as a result of irrigation with polluted water or deposition of animal manure, agrochemicals, and inorganic fertilizers [8,9], as well as wastewater filtration derived from industrial activities [10]. It appears that PTEs can enter forage crops and then the milk of dairy cattle that feed on that forage [9,11,12].

In addition to PTEs, polycyclic aromatic hydrocarbons (PAHs) are also widespread pollutants in soil, water, air, and plants [13–15]. They primarily result from the incomplete combustion or pyrolysis of organic materials, through incineration or industrial activities [4]. The U.S. Environmental Protection Agency categorizes 16 PAHs as priority pollutants due to their mutagenic and carcinogenic properties. PAHs can enter plants from the soil [16] and then transfer to the milk of dairy cows that eat the plants as forage, ultimately passing to humans who drink the milk [17–19]. In addition, the lipophilicity of PAHs may facilitate their accumulation in milk [20]. Considering this, the European Union has established maximum permissible limits for certain PAHs in certain foods likely to contain these contaminants. An example is milk and follow-on milk intended for infants, with a maximum permissible content of 1 μg L−<sup>1</sup> of benzo(a)pyrene or 1 μg L−<sup>1</sup> of the sum of benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene, and chrysene [21].

PTEs and PAHs frequently coexist in soils in proximity to highways and certain industries, such as the smelting and mining industries [22,23]. Therefore, it is quite important to assess the risk that milk produced from dairy farms near these areas may be contaminated with PAHs and PTEs. Northern Spain provides a good study area, since many dairy farms are located close to active industrial facilities. Here, we quantified several PTEs and PAHs of concern in soil, forage, and milk samples on farms near and farther from industrial areas in northern Spain, and we evaluated the transfer of these contaminants into milk.
