Hello,
a bit more of context could help but, I will make a try:
Mean: Valor medio (in this context)
DT50: It should be some parameter used for analysing the concentration of LAB in a certain soil.
LAB:Linear alkylbenzene
So, "Valor medio de DT50 de LAB en el terreno". El resto de la frase, no lo sé.
Saludos
María