The ratings of five chemicals stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Tronox Ltd.’s (TROX) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Tronox produces and markets titanium dioxide. The stock also earns F’s in Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, Equity and Margin Growth. To get an in-depth look at TROX, get Portfolio Grader’s complete analysis of TROX stock.

Calgon Carbon Corporation (CCC) earns a D this week, falling from last week’s grade of C. Calgon Carbon is engaged in products and services for purifying water and air. For more information, get Portfolio Grader’s complete analysis of CCC stock.

This week, OCI Partners LP’s (OCIP) rating worsens to a D from the company’s C rating a week ago. To get an in-depth look at OCIP, get Portfolio Grader’s complete analysis of OCIP stock.

Marrone Bio Innovations, Inc.’s (MBII) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). The stock receives F’s in Earnings Momentum, Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of MBII stock.

The rating of Rockwood Holdings, Inc. (ROC) declines this week from a C to a D. Rockwood Holdings is a global developer, manufacturer and marketer of value-added specialty chemicals and advanced materials used for industrial and commercial purposes. The stock gets F’s in Earnings Growth, Earnings Surprise and Margin Growth. To get an in-depth look at ROC, get Portfolio Grader’s complete analysis of ROC stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.